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This value is not locale-dependent. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.ascii_lowercase"> string.ascii_lowercase<a class="headerlink" href="#string.ascii_lowercase" title="Link to this definition">¶</a></dt> <dd>The lowercase letters <code class="docutils literal notranslate">'abcdefghijklmnopqrstuvwxyz'</code>. This value is not locale-dependent and will not change. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.ascii_uppercase"> string.ascii_uppercase<a class="headerlink" href="#string.ascii_uppercase" title="Link to this definition">¶</a></dt> <dd>The uppercase letters <code class="docutils literal notranslate">'ABCDEFGHIJKLMNOPQRSTUVWXYZ'</code>. This value is not locale-dependent and will not change. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.digits"> string.digits<a class="headerlink" href="#string.digits" title="Link to this definition">¶</a></dt> <dd>The string <code class="docutils literal notranslate">'0123456789'</code>. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.hexdigits"> string.hexdigits<a class="headerlink" href="#string.hexdigits" title="Link to this definition">¶</a></dt> <dd>The string <code class="docutils literal notranslate">'0123456789abcdefABCDEF'</code>. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.octdigits"> string.octdigits<a class="headerlink" href="#string.octdigits" title="Link to this definition">¶</a></dt> <dd>The string <code class="docutils literal notranslate">'01234567'</code>. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.punctuation"> string.punctuation<a class="headerlink" href="#string.punctuation" title="Link to this definition">¶</a></dt> <dd>String of ASCII characters which are considered punctuation characters in the <code class="docutils literal notranslate">C</code> locale: <code class="docutils literal notranslate">!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~</code>. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.printable"> string.printable<a class="headerlink" href="#string.printable" title="Link to this definition">¶</a></dt> <dd>String of ASCII characters which are considered printable by Python. This is a combination of <a class="reference internal" href="#string.digits" title="string.digits"><code class="xref py py-const docutils literal notranslate">digits</code></a>, <a class="reference internal" href="#string.ascii_letters" title="string.ascii_letters"><code class="xref py py-const docutils literal notranslate">ascii_letters</code></a>, <a class="reference internal" href="#string.punctuation" title="string.punctuation"><code class="xref py py-const docutils literal notranslate">punctuation</code></a>, and <a class="reference internal" href="#string.whitespace" title="string.whitespace"><code class="xref py py-const docutils literal notranslate">whitespace</code></a>. <div class="admonition note"> Note By design, <a class="reference internal" href="stdtypes.html#str.isprintable" title="str.isprintable"><code class="xref py py-meth docutils literal notranslate">string.printable.isprintable()</code></a> returns <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a>. In particular, <code class="docutils literal notranslate">string.printable</code> is not printable in the POSIX sense (see <a class="manpage reference external" href="https://manpages.debian.org/locale(5)">LC_CTYPE</a>). </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="string.whitespace"> string.whitespace<a class="headerlink" href="#string.whitespace" title="Link to this definition">¶</a></dt> <dd>A string containing all ASCII characters that are considered whitespace. This includes the characters space, tab, linefeed, return, formfeed, and vertical tab. </dd></dl> </section> <section id="custom-string-formatting"> <h2>Custom String Formatting<a class="headerlink" href="#custom-string-formatting" title="Link to this heading">¶</a></h2> The built-in string class provides the ability to do complex variable substitutions and value formatting via the <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">format()</code></a> method described in <a class="pep reference external" href="https://peps.python.org/pep-3101/">PEP 3101</a>. The <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> class in the <a class="reference internal" href="#module-string" title="string: Common string operations."><code class="xref py py-mod docutils literal notranslate">string</code></a> module allows you to create and customize your own string formatting behaviors using the same implementation as the built-in <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">format()</code></a> method. <dl class="py class"> <dt class="sig sig-object py" id="string.Formatter"> class string.Formatter<a class="headerlink" href="#string.Formatter" title="Link to this definition">¶</a></dt> <dd>The <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> class has the following public methods: <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.format"> format(format_string, <abbr title="Positional-only parameter separator (PEP 570)">/</abbr>, *args, **kwargs)<a class="headerlink" href="#string.Formatter.format" title="Link to this definition">¶</a></dt> <dd>The primary API method. It takes a format string and an arbitrary set of positional and keyword arguments. It is just a wrapper that calls <a class="reference internal" href="#string.Formatter.vformat" title="string.Formatter.vformat"><code class="xref py py-meth docutils literal notranslate">vformat()</code></a>. <div class="versionchanged"> Changed in version 3.7: A format string argument is now <a class="reference internal" href="../glossary.html#positional-only-parameter">positional-only</a>. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.vformat"> vformat(format_string, args, kwargs)<a class="headerlink" href="#string.Formatter.vformat" title="Link to this definition">¶</a></dt> <dd>This function does the actual work of formatting. It is exposed as a separate function for cases where you want to pass in a predefined dictionary of arguments, rather than unpacking and repacking the dictionary as individual arguments using the <code class="docutils literal notranslate">*args</code> and <code class="docutils literal notranslate">**kwargs</code> syntax. <a class="reference internal" href="#string.Formatter.vformat" title="string.Formatter.vformat"><code class="xref py py-meth docutils literal notranslate">vformat()</code></a> does the work of breaking up the format string into character data and replacement fields. It calls the various methods described below. </dd></dl> In addition, the <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> defines a number of methods that are intended to be replaced by subclasses: <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.parse"> parse(format_string)<a class="headerlink" href="#string.Formatter.parse" title="Link to this definition">¶</a></dt> <dd>Loop over the format_string and return an iterable of tuples (literal_text, field_name, format_spec, conversion). This is used by <a class="reference internal" href="#string.Formatter.vformat" title="string.Formatter.vformat"><code class="xref py py-meth docutils literal notranslate">vformat()</code></a> to break the string into either literal text, or replacement fields. The values in the tuple conceptually represent a span of literal text followed by a single replacement field. If there is no literal text (which can happen if two replacement fields occur consecutively), then literal_text will be a zero-length string. If there is no replacement field, then the values of field_name, format_spec and conversion will be <code class="docutils literal notranslate">None</code>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.get_field"> get_field(field_name, args, kwargs)<a class="headerlink" href="#string.Formatter.get_field" title="Link to this definition">¶</a></dt> <dd>Given field_name as returned by <a class="reference internal" href="#string.Formatter.parse" title="string.Formatter.parse"><code class="xref py py-meth docutils literal notranslate">parse()</code></a> (see above), convert it to an object to be formatted. Returns a tuple (obj, used_key). The default version takes strings of the form defined in <a class="pep reference external" href="https://peps.python.org/pep-3101/">PEP 3101</a>, such as “0[name]” or “label.title”. args and kwargs are as passed in to <a class="reference internal" href="#string.Formatter.vformat" title="string.Formatter.vformat"><code class="xref py py-meth docutils literal notranslate">vformat()</code></a>. The return value used_key has the same meaning as the key parameter to <a class="reference internal" href="#string.Formatter.get_value" title="string.Formatter.get_value"><code class="xref py py-meth docutils literal notranslate">get_value()</code></a>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.get_value"> get_value(key, args, kwargs)<a class="headerlink" href="#string.Formatter.get_value" title="Link to this definition">¶</a></dt> <dd>Retrieve a given field value. The key argument will be either an integer or a string. If it is an integer, it represents the index of the positional argument in args; if it is a string, then it represents a named argument in kwargs. The args parameter is set to the list of positional arguments to <a class="reference internal" href="#string.Formatter.vformat" title="string.Formatter.vformat"><code class="xref py py-meth docutils literal notranslate">vformat()</code></a>, and the kwargs parameter is set to the dictionary of keyword arguments. For compound field names, these functions are only called for the first component of the field name; subsequent components are handled through normal attribute and indexing operations. So for example, the field expression ‘0.name’ would cause <a class="reference internal" href="#string.Formatter.get_value" title="string.Formatter.get_value"><code class="xref py py-meth docutils literal notranslate">get_value()</code></a> to be called with a key argument of 0. The <code class="docutils literal notranslate">name</code> attribute will be looked up after <a class="reference internal" href="#string.Formatter.get_value" title="string.Formatter.get_value"><code class="xref py py-meth docutils literal notranslate">get_value()</code></a> returns by calling the built-in <a class="reference internal" href="functions.html#getattr" title="getattr"><code class="xref py py-func docutils literal notranslate">getattr()</code></a> function. If the index or keyword refers to an item that does not exist, then an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate">IndexError</code></a> or <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate">KeyError</code></a> should be raised. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.check_unused_args"> check_unused_args(used_args, args, kwargs)<a class="headerlink" href="#string.Formatter.check_unused_args" title="Link to this definition">¶</a></dt> <dd>Implement checking for unused arguments if desired. The arguments to this function is the set of all argument keys that were actually referred to in the format string (integers for positional arguments, and strings for named arguments), and a reference to the args and kwargs that was passed to vformat. The set of unused args can be calculated from these parameters. <a class="reference internal" href="#string.Formatter.check_unused_args" title="string.Formatter.check_unused_args"><code class="xref py py-meth docutils literal notranslate">check_unused_args()</code></a> is assumed to raise an exception if the check fails. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.format_field"> format_field(value, format_spec)<a class="headerlink" href="#string.Formatter.format_field" title="Link to this definition">¶</a></dt> <dd><a class="reference internal" href="#string.Formatter.format_field" title="string.Formatter.format_field"><code class="xref py py-meth docutils literal notranslate">format_field()</code></a> simply calls the global <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate">format()</code></a> built-in. The method is provided so that subclasses can override it. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Formatter.convert_field"> convert_field(value, conversion)<a class="headerlink" href="#string.Formatter.convert_field" title="Link to this definition">¶</a></dt> <dd>Converts the value (returned by <a class="reference internal" href="#string.Formatter.get_field" title="string.Formatter.get_field"><code class="xref py py-meth docutils literal notranslate">get_field()</code></a>) given a conversion type (as in the tuple returned by the <a class="reference internal" href="#string.Formatter.parse" title="string.Formatter.parse"><code class="xref py py-meth docutils literal notranslate">parse()</code></a> method). The default version understands ‘s’ (str), ‘r’ (repr) and ‘a’ (ascii) conversion types. </dd></dl> </dd></dl> </section> <section id="format-string-syntax"> <h2>Format String Syntax<a class="headerlink" href="#format-string-syntax" title="Link to this heading">¶</a></h2> The <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a> method and the <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> class share the same syntax for format strings (although in the case of <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a>, subclasses can define their own format string syntax). The syntax is related to that of <a class="reference internal" href="../reference/lexical_analysis.html#f-strings">formatted string literals</a>, but it is less sophisticated and, in particular, does not support arbitrary expressions. Format strings contain “replacement fields” surrounded by curly braces <code class="docutils literal notranslate">{}</code>. Anything that is not contained in braces is considered literal text, which is copied unchanged to the output. If you need to include a brace character in the literal text, it can be escaped by doubling: <code class="docutils literal notranslate">{{</code> and <code class="docutils literal notranslate">}}</code>. The grammar for a replacement field is as follows: <pre> replacement_field ::= "{" [<a class="reference internal" href="#grammar-token-format-string-field_name"><code class="xref docutils literal notranslate">field_name</code></a>] ["!" <a class="reference internal" href="#grammar-token-format-string-conversion"><code class="xref docutils literal notranslate">conversion</code></a>] [":" <a class="reference internal" href="#grammar-token-format-string-format_spec"><code class="xref docutils literal notranslate">format_spec</code></a>] "}" field_name ::= <a class="reference internal" href="#grammar-token-format-string-arg_name"><code class="xref docutils literal notranslate">arg_name</code></a> ("." <a class="reference internal" href="#grammar-token-format-string-attribute_name"><code class="xref docutils literal notranslate">attribute_name</code></a> | "[" <a class="reference internal" href="#grammar-token-format-string-element_index"><code class="xref docutils literal notranslate">element_index</code></a> "]")* arg_name ::= [<a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate">identifier</code></a> | <a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-digit"><code class="xref docutils literal notranslate">digit</code></a>+] attribute_name ::= <a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate">identifier</code></a> element_index ::= <a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-digit"><code class="xref docutils literal notranslate">digit</code></a>+ | <a class="reference internal" href="#grammar-token-format-string-index_string"><code class="xref docutils literal notranslate">index_string</code></a> index_string ::= <any source character except "]"> + conversion ::= "r" | "s" | "a" format_spec ::= <a class="reference internal" href="#grammar-token-format-spec-format_spec"><code class="xref docutils literal notranslate">format-spec:format_spec</code></a> </pre> In less formal terms, the replacement field can start with a field_name that specifies the object whose value is to be formatted and inserted into the output instead of the replacement field. The field_name is optionally followed by a conversion field, which is preceded by an exclamation point <code class="docutils literal notranslate">'!'</code>, and a format_spec, which is preceded by a colon <code class="docutils literal notranslate">':'</code>. These specify a non-default format for the replacement value. See also the <a class="reference internal" href="#formatspec">Format Specification Mini-Language</a> section. The field_name itself begins with an arg_name that is either a number or a keyword. If it’s a number, it refers to a positional argument, and if it’s a keyword, it refers to a named keyword argument. An arg_name is treated as a number if a call to <a class="reference internal" href="stdtypes.html#str.isdecimal" title="str.isdecimal"><code class="xref py py-meth docutils literal notranslate">str.isdecimal()</code></a> on the string would return true. If the numerical arg_names in a format string are 0, 1, 2, … in sequence, they can all be omitted (not just some) and the numbers 0, 1, 2, … will be automatically inserted in that order. Because arg_name is not quote-delimited, it is not possible to specify arbitrary dictionary keys (e.g., the strings <code class="docutils literal notranslate">'10'</code> or <code class="docutils literal notranslate">':-]'</code>) within a format string. The arg_name can be followed by any number of index or attribute expressions. An expression of the form <code class="docutils literal notranslate">'.name'</code> selects the named attribute using <a class="reference internal" href="functions.html#getattr" title="getattr"><code class="xref py py-func docutils literal notranslate">getattr()</code></a>, while an expression of the form <code class="docutils literal notranslate">'[index]'</code> does an index lookup using <a class="reference internal" href="../reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>. <div class="versionchanged"> Changed in version 3.1: The positional argument specifiers can be omitted for <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a>, so <code class="docutils literal notranslate">'{} {}'.format(a, b)</code> is equivalent to <code class="docutils literal notranslate">'{0} {1}'.format(a, b)</code>. </div> <div class="versionchanged"> Changed in version 3.4: The positional argument specifiers can be omitted for <a class="reference internal" href="#string.Formatter" title="string.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a>. </div> Some simple format string examples: <div class="highlight-python3 notranslate"><div class="highlight"><pre>"First, thou shalt count to {0}" # References first positional argument "Bring me a {}" # Implicitly references the first positional argument "From {} to {}" # Same as "From {0} to {1}" "My quest is {name}" # References keyword argument 'name' "Weight in tons {0.weight}" # 'weight' attribute of first positional arg "Units destroyed: {players[0]}" # First element of keyword argument 'players'. </pre></div> </div> The conversion field causes a type coercion before formatting. Normally, the job of formatting a value is done by the <a class="reference internal" href="../reference/datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate">__format__()</code></a> method of the value itself. However, in some cases it is desirable to force a type to be formatted as a string, overriding its own definition of formatting. By converting the value to a string before calling <a class="reference internal" href="../reference/datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate">__format__()</code></a>, the normal formatting logic is bypassed. Three conversion flags are currently supported: <code class="docutils literal notranslate">'!s'</code> which calls <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str()</code></a> on the value, <code class="docutils literal notranslate">'!r'</code> which calls <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate">repr()</code></a> and <code class="docutils literal notranslate">'!a'</code> which calls <a class="reference internal" href="functions.html#ascii" title="ascii"><code class="xref py py-func docutils literal notranslate">ascii()</code></a>. Some examples: <div class="highlight-python3 notranslate"><div class="highlight"><pre>"Harold's a clever {0!s}" # Calls str() on the argument first "Bring out the holy {name!r}" # Calls repr() on the argument first "More {!a}" # Calls ascii() on the argument first </pre></div> </div> The format_spec field contains a specification of how the value should be presented, including such details as field width, alignment, padding, decimal precision and so on. Each value type can define its own “formatting mini-language” or interpretation of the format_spec. Most built-in types support a common formatting mini-language, which is described in the next section. A format_spec field can also include nested replacement fields within it. These nested replacement fields may contain a field name, conversion flag and format specification, but deeper nesting is not allowed. The replacement fields within the format_spec are substituted before the format_spec string is interpreted. This allows the formatting of a value to be dynamically specified. See the <a class="reference internal" href="#formatexamples">Format examples</a> section for some examples. <section id="format-specification-mini-language"> <h3>Format Specification Mini-Language<a class="headerlink" href="#format-specification-mini-language" title="Link to this heading">¶</a></h3> “Format specifications” are used within replacement fields contained within a format string to define how individual values are presented (see <a class="reference internal" href="#formatstrings">Format String Syntax</a> and <a class="reference internal" href="../reference/lexical_analysis.html#f-strings">f-strings</a>). They can also be passed directly to the built-in <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate">format()</code></a> function. Each formattable type may define how the format specification is to be interpreted. Most built-in types implement the following options for format specifications, although some of the formatting options are only supported by the numeric types. A general convention is that an empty format specification produces the same result as if you had called <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str()</code></a> on the value. A non-empty format specification typically modifies the result. The general form of a standard format specifier is: <pre> format_spec ::= [[<a class="reference internal" href="#grammar-token-format-spec-fill"><code class="xref docutils literal notranslate">fill</code></a>]<a class="reference internal" href="#grammar-token-format-spec-align"><code class="xref docutils literal notranslate">align</code></a>][<a class="reference internal" href="#grammar-token-format-spec-sign"><code class="xref docutils literal notranslate">sign</code></a>]["z"]["#"]["0"][<a class="reference internal" href="#grammar-token-format-spec-width"><code class="xref docutils literal notranslate">width</code></a>][<a class="reference internal" href="#grammar-token-format-spec-grouping_option"><code class="xref docutils literal notranslate">grouping_option</code></a>]["." <a class="reference internal" href="#grammar-token-format-spec-precision"><code class="xref docutils literal notranslate">precision</code></a>][<a class="reference internal" href="#grammar-token-format-spec-type"><code class="xref docutils literal notranslate">type</code></a>] fill ::= <any character> align ::= "<" | ">" | "=" | "^" sign ::= "+" | "-" | " " width ::= <a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-digit"><code class="xref docutils literal notranslate">digit</code></a>+ grouping_option ::= "_" | "," precision ::= <a class="reference internal" href="../reference/lexical_analysis.html#grammar-token-python-grammar-digit"><code class="xref docutils literal notranslate">digit</code></a>+ type ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%" </pre> If a valid align value is specified, it can be preceded by a fill character that can be any character and defaults to a space if omitted. It is not possible to use a literal curly brace (”<code class="docutils literal notranslate">{</code>” or “<code class="docutils literal notranslate">}</code>”) as the fill character in a <a class="reference internal" href="../reference/lexical_analysis.html#f-strings">formatted string literal</a> or when using the <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a> method. However, it is possible to insert a curly brace with a nested replacement field. This limitation doesn’t affect the <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate">format()</code></a> function. The meaning of the various alignment options is as follows: <table class="docutils align-default" id="index-3"> <thead> <tr class="row-odd"><th class="head">Option</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">'<'</code></td> <td>Forces the field to be left-aligned within the available space (this is the default for most objects).</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'>'</code></td> <td>Forces the field to be right-aligned within the available space (this is the default for numbers).</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'='</code></td> <td>Forces the padding to be placed after the sign (if any) but before the digits. This is used for printing fields in the form ‘+000000120’. This alignment option is only valid for numeric types, excluding <a class="reference internal" href="functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate">complex</code></a>. It becomes the default for numbers when ‘0’ immediately precedes the field width.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'^'</code></td> <td>Forces the field to be centered within the available space.</td> </tr> </tbody> </table> Note that unless a minimum field width is defined, the field width will always be the same size as the data to fill it, so that the alignment option has no meaning in this case. The sign option is only valid for number types, and can be one of the following: <table class="docutils align-default" id="index-4"> <thead> <tr class="row-odd"><th class="head">Option</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">'+'</code></td> <td>indicates that a sign should be used for both positive as well as negative numbers.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'-'</code></td> <td>indicates that a sign should be used only for negative numbers (this is the default behavior).</td> </tr> <tr class="row-even"><td>space</td> <td>indicates that a leading space should be used on positive numbers, and a minus sign on negative numbers.</td> </tr> </tbody> </table> The <code class="docutils literal notranslate">'z'</code> option coerces negative zero floating-point values to positive zero after rounding to the format precision. This option is only valid for floating-point presentation types. <div class="versionchanged"> Changed in version 3.11: Added the <code class="docutils literal notranslate">'z'</code> option (see also <a class="pep reference external" href="https://peps.python.org/pep-0682/">PEP 682</a>). </div> The <code class="docutils literal notranslate">'#'</code> option causes the “alternate form” to be used for the conversion. The alternate form is defined differently for different types. This option is only valid for integer, float and complex types. For integers, when binary, octal, or hexadecimal output is used, this option adds the respective prefix <code class="docutils literal notranslate">'0b'</code>, <code class="docutils literal notranslate">'0o'</code>, <code class="docutils literal notranslate">'0x'</code>, or <code class="docutils literal notranslate">'0X'</code> to the output value. For float and complex the alternate form causes the result of the conversion to always contain a decimal-point character, even if no digits follow it. Normally, a decimal-point character appears in the result of these conversions only if a digit follows it. In addition, for <code class="docutils literal notranslate">'g'</code> and <code class="docutils literal notranslate">'G'</code> conversions, trailing zeros are not removed from the result. The <code class="docutils literal notranslate">','</code> option signals the use of a comma for a thousands separator for floating-point presentation types and for integer presentation type <code class="docutils literal notranslate">'d'</code>. For other presentation types, this option is an error. For a locale aware separator, use the <code class="docutils literal notranslate">'n'</code> integer presentation type instead. <div class="versionchanged"> Changed in version 3.1: Added the <code class="docutils literal notranslate">','</code> option (see also <a class="pep reference external" href="https://peps.python.org/pep-0378/">PEP 378</a>). </div> The <code class="docutils literal notranslate">'_'</code> option signals the use of an underscore for a thousands separator for floating-point presentation types and for integer presentation type <code class="docutils literal notranslate">'d'</code>. For integer presentation types <code class="docutils literal notranslate">'b'</code>, <code class="docutils literal notranslate">'o'</code>, <code class="docutils literal notranslate">'x'</code>, and <code class="docutils literal notranslate">'X'</code>, underscores will be inserted every 4 digits. For other presentation types, specifying this option is an error. <div class="versionchanged"> Changed in version 3.6: Added the <code class="docutils literal notranslate">'_'</code> option (see also <a class="pep reference external" href="https://peps.python.org/pep-0515/">PEP 515</a>). </div> width is a decimal integer defining the minimum total field width, including any prefixes, separators, and other formatting characters. If not specified, then the field width will be determined by the content. When no explicit alignment is given, preceding the width field by a zero (<code class="docutils literal notranslate">'0'</code>) character enables sign-aware zero-padding for numeric types, excluding <a class="reference internal" href="functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate">complex</code></a>. This is equivalent to a fill character of <code class="docutils literal notranslate">'0'</code> with an alignment type of <code class="docutils literal notranslate">'='</code>. <div class="versionchanged"> Changed in version 3.10: Preceding the width field by <code class="docutils literal notranslate">'0'</code> no longer affects the default alignment for strings. </div> The precision is a decimal integer indicating how many digits should be displayed after the decimal point for presentation types <code class="docutils literal notranslate">'f'</code> and <code class="docutils literal notranslate">'F'</code>, or before and after the decimal point for presentation types <code class="docutils literal notranslate">'g'</code> or <code class="docutils literal notranslate">'G'</code>. For string presentation types the field indicates the maximum field size - in other words, how many characters will be used from the field content. The precision is not allowed for integer presentation types. Finally, the type determines how the data should be presented. The available string presentation types are: <blockquote> <div><table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Type</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">'s'</code></td> <td>String format. This is the default type for strings and may be omitted.</td> </tr> <tr class="row-odd"><td>None</td> <td>The same as <code class="docutils literal notranslate">'s'</code>.</td> </tr> </tbody> </table> </div></blockquote> The available integer presentation types are: <blockquote> <div><table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Type</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">'b'</code></td> <td>Binary format. Outputs the number in base 2.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'c'</code></td> <td>Character. Converts the integer to the corresponding unicode character before printing.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'d'</code></td> <td>Decimal Integer. Outputs the number in base 10.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'o'</code></td> <td>Octal format. Outputs the number in base 8.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'x'</code></td> <td>Hex format. Outputs the number in base 16, using lower-case letters for the digits above 9.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'X'</code></td> <td>Hex format. Outputs the number in base 16, using upper-case letters for the digits above 9. In case <code class="docutils literal notranslate">'#'</code> is specified, the prefix <code class="docutils literal notranslate">'0x'</code> will be upper-cased to <code class="docutils literal notranslate">'0X'</code> as well.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'n'</code></td> <td>Number. This is the same as <code class="docutils literal notranslate">'d'</code>, except that it uses the current locale setting to insert the appropriate number separator characters.</td> </tr> <tr class="row-odd"><td>None</td> <td>The same as <code class="docutils literal notranslate">'d'</code>.</td> </tr> </tbody> </table> </div></blockquote> In addition to the above presentation types, integers can be formatted with the floating-point presentation types listed below (except <code class="docutils literal notranslate">'n'</code> and <code class="docutils literal notranslate">None</code>). When doing so, <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-func docutils literal notranslate">float()</code></a> is used to convert the integer to a floating-point number before formatting. The available presentation types for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> and <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a> values are: <blockquote> <div><table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Type</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">'e'</code></td> <td>Scientific notation. For a given precision <code class="docutils literal notranslate">p</code>, formats the number in scientific notation with the letter ‘e’ separating the coefficient from the exponent. The coefficient has one digit before and <code class="docutils literal notranslate">p</code> digits after the decimal point, for a total of <code class="docutils literal notranslate">p + 1</code> significant digits. With no precision given, uses a precision of <code class="docutils literal notranslate">6</code> digits after the decimal point for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>, and shows all coefficient digits for <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a>. If <code class="docutils literal notranslate">p=0</code>, the decimal point is omitted unless the <code class="docutils literal notranslate">#</code> option is used.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'E'</code></td> <td>Scientific notation. Same as <code class="docutils literal notranslate">'e'</code> except it uses an upper case ‘E’ as the separator character.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'f'</code></td> <td>Fixed-point notation. For a given precision <code class="docutils literal notranslate">p</code>, formats the number as a decimal number with exactly <code class="docutils literal notranslate">p</code> digits following the decimal point. With no precision given, uses a precision of <code class="docutils literal notranslate">6</code> digits after the decimal point for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>, and uses a precision large enough to show all coefficient digits for <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a>. If <code class="docutils literal notranslate">p=0</code>, the decimal point is omitted unless the <code class="docutils literal notranslate">#</code> option is used.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'F'</code></td> <td>Fixed-point notation. Same as <code class="docutils literal notranslate">'f'</code>, but converts <code class="docutils literal notranslate">nan</code> to <code class="docutils literal notranslate">NAN</code> and <code class="docutils literal notranslate">inf</code> to <code class="docutils literal notranslate">INF</code>.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'g'</code></td> <td>General format. For a given precision <code class="docutils literal notranslate">p >= 1</code>, this rounds the number to <code class="docutils literal notranslate">p</code> significant digits and then formats the result in either fixed-point format or in scientific notation, depending on its magnitude. A precision of <code class="docutils literal notranslate">0</code> is treated as equivalent to a precision of <code class="docutils literal notranslate">1</code>. The precise rules are as follows: suppose that the result formatted with presentation type <code class="docutils literal notranslate">'e'</code> and precision <code class="docutils literal notranslate">p-1</code> would have exponent <code class="docutils literal notranslate">exp</code>. Then, if <code class="docutils literal notranslate">m <= exp < p</code>, where <code class="docutils literal notranslate">m</code> is -4 for floats and -6 for <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimals</code></a>, the number is formatted with presentation type <code class="docutils literal notranslate">'f'</code> and precision <code class="docutils literal notranslate">p-1-exp</code>. Otherwise, the number is formatted with presentation type <code class="docutils literal notranslate">'e'</code> and precision <code class="docutils literal notranslate">p-1</code>. In both cases insignificant trailing zeros are removed from the significand, and the decimal point is also removed if there are no remaining digits following it, unless the <code class="docutils literal notranslate">'#'</code> option is used. With no precision given, uses a precision of <code class="docutils literal notranslate">6</code> significant digits for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>. For <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a>, the coefficient of the result is formed from the coefficient digits of the value; scientific notation is used for values smaller than <code class="docutils literal notranslate">1e-6</code> in absolute value and values where the place value of the least significant digit is larger than 1, and fixed-point notation is used otherwise. Positive and negative infinity, positive and negative zero, and nans, are formatted as <code class="docutils literal notranslate">inf</code>, <code class="docutils literal notranslate">-inf</code>, <code class="docutils literal notranslate">0</code>, <code class="docutils literal notranslate">-0</code> and <code class="docutils literal notranslate">nan</code> respectively, regardless of the precision. </td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'G'</code></td> <td>General format. Same as <code class="docutils literal notranslate">'g'</code> except switches to <code class="docutils literal notranslate">'E'</code> if the number gets too large. The representations of infinity and NaN are uppercased, too.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">'n'</code></td> <td>Number. This is the same as <code class="docutils literal notranslate">'g'</code>, except that it uses the current locale setting to insert the appropriate number separator characters.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">'%'</code></td> <td>Percentage. Multiplies the number by 100 and displays in fixed (<code class="docutils literal notranslate">'f'</code>) format, followed by a percent sign.</td> </tr> <tr class="row-even"><td>None</td> <td>For <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> this is like the <code class="docutils literal notranslate">'g'</code> type, except that when fixed-point notation is used to format the result, it always includes at least one digit past the decimal point, and switches to the scientific notation when <code class="docutils literal notranslate">exp >= p - 1</code>. When the precision is not specified, the latter will be as large as needed to represent the given value faithfully. For <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a>, this is the same as either <code class="docutils literal notranslate">'g'</code> or <code class="docutils literal notranslate">'G'</code> depending on the value of <code class="docutils literal notranslate">context.capitals</code> for the current decimal context. The overall effect is to match the output of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str()</code></a> as altered by the other format modifiers. </td> </tr> </tbody> </table> </div></blockquote> The result should be correctly rounded to a given precision <code class="docutils literal notranslate">p</code> of digits after the decimal point. The rounding mode for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> matches that of the <a class="reference internal" href="functions.html#round" title="round"><code class="xref py py-func docutils literal notranslate">round()</code></a> builtin. For <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate">Decimal</code></a>, the rounding mode of the current <a class="reference internal" href="decimal.html#decimal-context">context</a> will be used. The available presentation types for <a class="reference internal" href="functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate">complex</code></a> are the same as those for <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> (<code class="docutils literal notranslate">'%'</code> is not allowed). Both the real and imaginary components of a complex number are formatted as floating-point numbers, according to the specified presentation type. They are separated by the mandatory sign of the imaginary part, the latter being terminated by a <code class="docutils literal notranslate">j</code> suffix. If the presentation type is missing, the result will match the output of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str()</code></a> (complex numbers with a non-zero real part are also surrounded by parentheses), possibly altered by other format modifiers. </section> <section id="format-examples"> <h3>Format examples<a class="headerlink" href="#format-examples" title="Link to this heading">¶</a></h3> This section contains examples of the <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a> syntax and comparison with the old <code class="docutils literal notranslate">%</code>-formatting. In most of the cases the syntax is similar to the old <code class="docutils literal notranslate">%</code>-formatting, with the addition of the <code class="docutils literal notranslate">{}</code> and with <code class="docutils literal notranslate">:</code> used instead of <code class="docutils literal notranslate">%</code>. For example, <code class="docutils literal notranslate">'%03.2f'</code> can be translated to <code class="docutils literal notranslate">'{:03.2f}'</code>. The new format syntax also supports new and different options, shown in the following examples. Accessing arguments by position: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> '{0}, {1}, {2}'.format('a', 'b', 'c') 'a, b, c' >>> '{}, {}, {}'.format('a', 'b', 'c') # 3.1+ only 'a, b, c' >>> '{2}, {1}, {0}'.format('a', 'b', 'c') 'c, b, a' >>> '{2}, {1}, {0}'.format(*'abc') # unpacking argument sequence 'c, b, a' >>> '{0}{1}{0}'.format('abra', 'cad') # arguments' indices can be repeated 'abracadabra' </pre></div> </div> Accessing arguments by name: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W') 'Coordinates: 37.24N, -115.81W' >>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'} >>> 'Coordinates: {latitude}, {longitude}'.format(**coord) 'Coordinates: 37.24N, -115.81W' </pre></div> </div> Accessing arguments’ attributes: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> c = 3-5j >>> ('The complex number {0} is formed from the real part {0.real} ' ... 'and the imaginary part {0.imag}.').format(c) 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0.' >>> class Point: ... def __init__(self, x, y): ... self.x, self.y = x, y ... def __str__(self): ... return 'Point({self.x}, {self.y})'.format(self=self) ... >>> str(Point(4, 2)) 'Point(4, 2)' </pre></div> </div> Accessing arguments’ items: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> coord = (3, 5) >>> 'X: {0[0]}; Y: {0[1]}'.format(coord) 'X: 3; Y: 5' </pre></div> </div> Replacing <code class="docutils literal notranslate">%s</code> and <code class="docutils literal notranslate">%r</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2') "repr() shows quotes: 'test1'; str() doesn't: test2" </pre></div> </div> Aligning the text and specifying a width: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> '{:<30}'.format('left aligned') 'left aligned ' >>> '{:>30}'.format('right aligned') ' right aligned' >>> '{:^30}'.format('centered') ' centered ' >>> '{:*^30}'.format('centered') # use '*' as a fill char '***********centered***********' </pre></div> </div> Replacing <code class="docutils literal notranslate">%+f</code>, <code class="docutils literal notranslate">%-f</code>, and <code class="docutils literal notranslate">% f</code> and specifying a sign: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> '{:+f}; {:+f}'.format(3.14, -3.14) # show it always '+3.140000; -3.140000' >>> '{: f}; {: f}'.format(3.14, -3.14) # show a space for positive numbers ' 3.140000; -3.140000' >>> '{:-f}; {:-f}'.format(3.14, -3.14) # show only the minus -- same as '{:f}; {:f}' '3.140000; -3.140000' </pre></div> </div> Replacing <code class="docutils literal notranslate">%x</code> and <code class="docutils literal notranslate">%o</code> and converting the value to different bases: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> # format also supports binary numbers >>> "int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}".format(42) 'int: 42; hex: 2a; oct: 52; bin: 101010' >>> # with 0x, 0o, or 0b as prefix: >>> "int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}".format(42) 'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010' </pre></div> </div> Using the comma as a thousands separator: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> '{:,}'.format(1234567890) '1,234,567,890' </pre></div> </div> Expressing a percentage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> points = 19 >>> total = 22 >>> 'Correct answers: {:.2%}'.format(points/total) 'Correct answers: 86.36%' </pre></div> </div> Using type-specific formatting: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> import datetime >>> d = datetime.datetime(2010, 7, 4, 12, 15, 58) >>> '{:%Y-%m-%d %H:%M:%S}'.format(d) '2010-07-04 12:15:58' </pre></div> </div> Nesting arguments and more complex examples: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> for align, text in zip('<^>', ['left', 'center', 'right']): ... '{0:{fill}{align}16}'.format(text, fill=align, align=align) ... 'left<<<<<<<<<<<<' '^^^^^center^^^^^' '>>>>>>>>>>>right' >>> >>> octets = [192, 168, 0, 1] >>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets) 'C0A80001' >>> int(_, 16) 3232235521 >>> >>> width = 5 >>> for num in range(5,12): ... for base in 'dXob': ... print('{0:{width}{base}}'.format(num, base=base, width=width), end=' ') ... print() ... 5 5 5 101 6 6 6 110 7 7 7 111 8 8 10 1000 9 9 11 1001 10 A 12 1010 11 B 13 1011 </pre></div> </div> </section> </section> <section id="template-strings"> <h2>Template strings<a class="headerlink" href="#template-strings" title="Link to this heading">¶</a></h2> Template strings provide simpler string substitutions as described in <a class="pep reference external" href="https://peps.python.org/pep-0292/">PEP 292</a>. A primary use case for template strings is for internationalization (i18n) since in that context, the simpler syntax and functionality makes it easier to translate than other built-in string formatting facilities in Python. As an example of a library built on template strings for i18n, see the <a class="reference external" href="https://flufli18n.readthedocs.io/en/latest/">flufl.i18n</a> package. Template strings support <code class="docutils literal notranslate">$</code>-based substitutions, using the following rules: <ul class="simple"> <li><code class="docutils literal notranslate">$$</code> is an escape; it is replaced with a single <code class="docutils literal notranslate">$</code>.</li> <li><code class="docutils literal notranslate">$identifier</code> names a substitution placeholder matching a mapping key of <code class="docutils literal notranslate">"identifier"</code>. By default, <code class="docutils literal notranslate">"identifier"</code> is restricted to any case-insensitive ASCII alphanumeric string (including underscores) that starts with an underscore or ASCII letter. The first non-identifier character after the <code class="docutils literal notranslate">$</code> character terminates this placeholder specification.</li> <li><code class="docutils literal notranslate">${identifier}</code> is equivalent to <code class="docutils literal notranslate">$identifier</code>. It is required when valid identifier characters follow the placeholder but are not part of the placeholder, such as <code class="docutils literal notranslate">"${noun}ification"</code>.</li> </ul> Any other appearance of <code class="docutils literal notranslate">$</code> in the string will result in a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> being raised. The <a class="reference internal" href="#module-string" title="string: Common string operations."><code class="xref py py-mod docutils literal notranslate">string</code></a> module provides a <a class="reference internal" href="#string.Template" title="string.Template"><code class="xref py py-class docutils literal notranslate">Template</code></a> class that implements these rules. The methods of <a class="reference internal" href="#string.Template" title="string.Template"><code class="xref py py-class docutils literal notranslate">Template</code></a> are: <dl class="py class"> <dt class="sig sig-object py" id="string.Template"> class string.Template(template)<a class="headerlink" href="#string.Template" title="Link to this definition">¶</a></dt> <dd>The constructor takes a single argument which is the template string. <dl class="py method"> <dt class="sig sig-object py" id="string.Template.substitute"> substitute(mapping={}, <abbr title="Positional-only parameter separator (PEP 570)">/</abbr>, **kwds)<a class="headerlink" href="#string.Template.substitute" title="Link to this definition">¶</a></dt> <dd>Performs the template substitution, returning a new string. mapping is any dictionary-like object with keys that match the placeholders in the template. Alternatively, you can provide keyword arguments, where the keywords are the placeholders. When both mapping and kwds are given and there are duplicates, the placeholders from kwds take precedence. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Template.safe_substitute"> safe_substitute(mapping={}, <abbr title="Positional-only parameter separator (PEP 570)">/</abbr>, **kwds)<a class="headerlink" href="#string.Template.safe_substitute" title="Link to this definition">¶</a></dt> <dd>Like <a class="reference internal" href="#string.Template.substitute" title="string.Template.substitute"><code class="xref py py-meth docutils literal notranslate">substitute()</code></a>, except that if placeholders are missing from mapping and kwds, instead of raising a <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate">KeyError</code></a> exception, the original placeholder will appear in the resulting string intact. Also, unlike with <a class="reference internal" href="#string.Template.substitute" title="string.Template.substitute"><code class="xref py py-meth docutils literal notranslate">substitute()</code></a>, any other appearances of the <code class="docutils literal notranslate">$</code> will simply return <code class="docutils literal notranslate">$</code> instead of raising <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>. While other exceptions may still occur, this method is called “safe” because it always tries to return a usable string instead of raising an exception. In another sense, <a class="reference internal" href="#string.Template.safe_substitute" title="string.Template.safe_substitute"><code class="xref py py-meth docutils literal notranslate">safe_substitute()</code></a> may be anything other than safe, since it will silently ignore malformed templates containing dangling delimiters, unmatched braces, or placeholders that are not valid Python identifiers. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Template.is_valid"> is_valid()<a class="headerlink" href="#string.Template.is_valid" title="Link to this definition">¶</a></dt> <dd>Returns false if the template has invalid placeholders that will cause <a class="reference internal" href="#string.Template.substitute" title="string.Template.substitute"><code class="xref py py-meth docutils literal notranslate">substitute()</code></a> to raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="string.Template.get_identifiers"> get_identifiers()<a class="headerlink" href="#string.Template.get_identifiers" title="Link to this definition">¶</a></dt> <dd>Returns a list of the valid identifiers in the template, in the order they first appear, ignoring any invalid identifiers. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <a class="reference internal" href="#string.Template" title="string.Template"><code class="xref py py-class docutils literal notranslate">Template</code></a> instances also provide one public data attribute: <dl class="py attribute"> <dt class="sig sig-object py" id="string.Template.template"> template<a class="headerlink" href="#string.Template.template" title="Link to this definition">¶</a></dt> <dd>This is the object passed to the constructor’s template argument. In general, you shouldn’t change it, but read-only access is not enforced. </dd></dl> </dd></dl> Here is an example of how to use a Template: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> from string import Template >>> s = Template('$who likes $what') >>> s.substitute(who='tim', what='kung pao') 'tim likes kung pao' >>> d = dict(who='tim') >>> Template('Give $who $100').substitute(d) Traceback (most recent call last): ... ValueError: Invalid placeholder in string: line 1, col 11 >>> Template('$who likes $what').substitute(d) Traceback (most recent call last): ... KeyError: 'what' >>> Template('$who likes $what').safe_substitute(d) 'tim likes $what' </pre></div> </div> Advanced usage: you can derive subclasses of <a class="reference internal" href="#string.Template" title="string.Template"><code class="xref py py-class docutils literal notranslate">Template</code></a> to customize the placeholder syntax, delimiter character, or the entire regular expression used to parse template strings. To do this, you can override these class attributes: <ul> <li>delimiter – This is the literal string describing a placeholder introducing delimiter. The default value is <code class="docutils literal notranslate">$</code>. Note that this should not be a regular expression, as the implementation will call <a class="reference internal" href="re.html#re.escape" title="re.escape"><code class="xref py py-meth docutils literal notranslate">re.escape()</code></a> on this string as needed. Note further that you cannot change the delimiter after class creation (i.e. a different delimiter must be set in the subclass’s class namespace).</li> <li>idpattern – This is the regular expression describing the pattern for non-braced placeholders. The default value is the regular expression <code class="docutils literal notranslate">(?a:[_a-z][_a-z0-9]*)</code>. If this is given and braceidpattern is <code class="docutils literal notranslate">None</code> this pattern will also apply to braced placeholders. <div class="admonition note"> Note Since default flags is <code class="docutils literal notranslate">re.IGNORECASE</code>, pattern <code class="docutils literal notranslate">[a-z]</code> can match with some non-ASCII characters. That’s why we use the local <code class="docutils literal notranslate">a</code> flag here. </div> <div class="versionchanged"> Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and outside the braces. </div> </li> <li>braceidpattern – This is like idpattern but describes the pattern for braced placeholders. Defaults to <code class="docutils literal notranslate">None</code> which means to fall back to idpattern (i.e. the same pattern is used both inside and outside braces). If given, this allows you to define different patterns for braced and unbraced placeholders. <div class="versionadded"> Added in version 3.7. </div> </li> <li>flags – The regular expression flags that will be applied when compiling the regular expression used for recognizing substitutions. The default value is <code class="docutils literal notranslate">re.IGNORECASE</code>. Note that <code class="docutils literal notranslate">re.VERBOSE</code> will always be added to the flags, so custom idpatterns must follow conventions for verbose regular expressions. <div class="versionadded"> Added in version 3.2. </div> </li> </ul> Alternatively, you can provide the entire regular expression pattern by overriding the class attribute pattern. If you do this, the value must be a regular expression object with four named capturing groups. The capturing groups correspond to the rules given above, along with the invalid placeholder rule: <ul class="simple"> <li>escaped – This group matches the escape sequence, e.g. <code class="docutils literal notranslate">$$</code>, in the default pattern.</li> <li>named – This group matches the unbraced placeholder name; it should not include the delimiter in capturing group.</li> <li>braced – This group matches the brace enclosed placeholder name; it should not include either the delimiter or braces in the capturing group.</li> <li>invalid – This group matches any other delimiter pattern (usually a single delimiter), and it should appear last in the regular expression.</li> </ul> The methods on this class will raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> if the pattern matches the template without one of these named groups matching. </section> <section id="helper-functions"> <h2>Helper functions<a class="headerlink" href="#helper-functions" title="Link to this heading">¶</a></h2> <dl class="py function"> <dt class="sig sig-object py" id="string.capwords"> string.capwords(s, sep=None)<a class="headerlink" href="#string.capwords" title="Link to this definition">¶</a></dt> <dd>Split the argument into words using <a class="reference internal" href="stdtypes.html#str.split" title="str.split"><code class="xref py py-meth docutils literal notranslate">str.split()</code></a>, capitalize each word using <a class="reference internal" href="stdtypes.html#str.capitalize" title="str.capitalize"><code class="xref py py-meth docutils literal notranslate">str.capitalize()</code></a>, and join the capitalized words using <a class="reference internal" href="stdtypes.html#str.join" title="str.join"><code class="xref py py-meth docutils literal notranslate">str.join()</code></a>. If the optional second argument sep is absent or <code class="docutils literal notranslate">None</code>, runs of whitespace characters are replaced by a single space and leading and trailing whitespace are removed, otherwise sep is used to split and join the words. </dd></dl> </section> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate">string</code> — Common string operations</a><ul> <li><a class="reference internal" href="#string-constants">String constants</a></li> <li><a class="reference internal" href="#custom-string-formatting">Custom String Formatting</a></li> <li><a class="reference internal" href="#format-string-syntax">Format String Syntax</a><ul> <li><a class="reference internal" href="#format-specification-mini-language">Format Specification Mini-Language</a></li> <li><a class="reference internal" href="#format-examples">Format examples</a></li> </ul> </li> <li><a class="reference internal" href="#template-strings">Template strings</a></li> <li><a class="reference internal" href="#helper-functions">Helper functions</a></li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="text.html" title="previous chapter">Text Processing Services</a> </div> <div> <h4>Next topic</h4> <a href="re.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate">re</code> — Regular expression operations</a> </div> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/main/Doc/library/string.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> <div id="sidebarbutton" title="Collapse sidebar"> « </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="Related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="re.html" title="re — Regular expression operations" >next</a> |</li> <li class="right" > <a href="text.html" title="Text Processing Services" >previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.13.2 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="text.html" >Text Processing Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate">string</code> — Common string operations</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="footer"> © <a href="../copyright.html"> Copyright </a> 2001-2025, Python Software Foundation. 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