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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="color-scheme" content="light dark"> <title>PEP 290 – Code Migration and Modernization | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0290/"> <link rel="stylesheet" href="../_static/style.css" type="text/css"> <link rel="stylesheet" href="../_static/mq.css" type="text/css"> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" media="(prefers-color-scheme: light)" id="pyg-light"> <link rel="stylesheet" href="../_static/pygments_dark.css" type="text/css" media="(prefers-color-scheme: dark)" id="pyg-dark"> <link rel="alternate" type="application/rss+xml" title="Latest PEPs" href="https://peps.python.org/peps.rss"> <meta property="og:title" content='PEP 290 – Code Migration and Modernization | peps.python.org'> <meta property="og:description" 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<svg aria-hidden="true" class="colour-scheme-icon-when-dark"><use href="#svg-moon"></use></svg> <svg aria-hidden="true" class="colour-scheme-icon-when-light"><use href="#svg-sun"></use></svg> Toggle light / dark / auto colour theme </button> </header> <article> <section id="pep-content"> <h1 class="page-title">PEP 290 – Code Migration and Modernization</h1> <dl class="rfc2822 field-list simple"> <dt class="field-odd">Author:</dt> <dd class="field-odd">Raymond Hettinger <python at rcn.com></dd> <dt class="field-even">Status:</dt> <dd class="field-even"><abbr title="Currently valid informational guidance, or an in-use process">Active</abbr></dd> <dt class="field-odd">Type:</dt> <dd class="field-odd"><abbr title="Non-normative PEP containing background, guidelines or other information relevant to the Python ecosystem">Informational</abbr></dd> <dt class="field-even">Created:</dt> <dd class="field-even">06-Jun-2002</dd> <dt class="field-odd">Post-History:</dt> <dd class="field-odd"></dd> </dl> <hr class="docutils" /> <section id="contents"> <details><summary>Table of Contents</summary><ul class="simple"> <li><a class="reference internal" href="#abstract">Abstract</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#guidelines-for-new-entries">Guidelines for New Entries</a></li> <li><a class="reference internal" href="#migration-issues">Migration Issues</a><ul> <li><a class="reference internal" href="#comparison-operators-not-a-shortcut-for-producing-0-or-1">Comparison Operators Not a Shortcut for Producing 0 or 1</a></li> </ul> </li> <li><a class="reference internal" href="#modernization-procedures">Modernization Procedures</a><ul> <li><a class="reference internal" href="#python-2-4-or-later">Python 2.4 or Later</a><ul> <li><a class="reference internal" href="#inserting-and-popping-at-the-beginning-of-lists">Inserting and Popping at the Beginning of Lists</a></li> <li><a class="reference internal" href="#simplifying-custom-sorts">Simplifying Custom Sorts</a></li> <li><a class="reference internal" href="#replacing-common-uses-of-lambda">Replacing Common Uses of Lambda</a></li> <li><a class="reference internal" href="#simplified-reverse-iteration">Simplified Reverse Iteration</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-3-or-later">Python 2.3 or Later</a><ul> <li><a class="reference internal" href="#testing-string-membership">Testing String Membership</a></li> <li><a class="reference internal" href="#replace-apply-with-a-direct-function-call">Replace apply() with a Direct Function Call</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-2-or-later">Python 2.2 or Later</a><ul> <li><a class="reference internal" href="#testing-dictionary-membership">Testing Dictionary Membership</a></li> <li><a class="reference internal" href="#looping-over-dictionaries">Looping Over Dictionaries</a></li> <li><a class="reference internal" href="#stat-methods"><code class="docutils literal notranslate">stat</code> Methods</a></li> <li><a class="reference internal" href="#reduce-dependency-on-types-module">Reduce Dependency on <code class="docutils literal notranslate">types</code> Module</a></li> <li><a class="reference internal" href="#avoid-variable-names-that-clash-with-the-builtins-module">Avoid Variable Names that Clash with the <code class="docutils literal notranslate">__builtins__</code> Module</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-1-or-later">Python 2.1 or Later</a><ul> <li><a class="reference internal" href="#whrandom-module-deprecated"><code class="docutils literal notranslate">whrandom</code> Module Deprecated</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-0-or-later">Python 2.0 or Later</a><ul> <li><a class="reference internal" href="#string-methods">String Methods</a></li> <li><a class="reference internal" href="#startswith-and-endswith-string-methods"><code class="docutils literal notranslate">startswith</code> and <code class="docutils literal notranslate">endswith</code> String Methods</a></li> <li><a class="reference internal" href="#the-atexit-module">The <code class="docutils literal notranslate">atexit</code> Module</a></li> </ul> </li> <li><a class="reference internal" href="#python-1-5-or-later">Python 1.5 or Later</a><ul> <li><a class="reference internal" href="#class-based-exceptions">Class-Based Exceptions</a></li> </ul> </li> <li><a class="reference internal" href="#all-python-versions">All Python Versions</a><ul> <li><a class="reference internal" href="#testing-for-none">Testing for <code class="docutils literal notranslate">None</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#copyright">Copyright</a></li> </ul> </details></section> <section id="abstract"> <h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2> This PEP is a collection of procedures and ideas for updating Python applications when newer versions of Python are installed. The migration tips highlight possible areas of incompatibility and make suggestions on how to find and resolve those differences. The modernization procedures show how older code can be updated to take advantage of new language features. </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> This repository of procedures serves as a catalog or checklist of known migration issues and procedures for addressing those issues. Migration issues can arise for several reasons. Some obsolete features are slowly deprecated according to the guidelines in <a class="pep reference internal" href="../pep-0004/" title="PEP 4 – Deprecation of Standard Modules">PEP 4</a>. Also, some code relies on undocumented behaviors which are subject to change between versions. Some code may rely on behavior which was subsequently shown to be a bug and that behavior changes when the bug is fixed. Modernization options arise when new versions of Python add features that allow improved clarity or higher performance than previously available. </section> <section id="guidelines-for-new-entries"> <h2><a class="toc-backref" href="#guidelines-for-new-entries" role="doc-backlink">Guidelines for New Entries</a></h2> Developers with commit access may update this PEP directly. Others can send their ideas to a developer for possible inclusion. While a consistent format makes the repository easier to use, feel free to add or subtract sections to improve clarity. Grep patterns may be supplied as tool to help maintainers locate code for possible updates. However, fully automated search/replace style regular expressions are not recommended. Instead, each code fragment should be evaluated individually. The contra-indications section is the most important part of a new entry. It lists known situations where the update SHOULD NOT be applied. </section> <section id="migration-issues"> <h2><a class="toc-backref" href="#migration-issues" role="doc-backlink">Migration Issues</a></h2> <section id="comparison-operators-not-a-shortcut-for-producing-0-or-1"> <h3><a class="toc-backref" href="#comparison-operators-not-a-shortcut-for-producing-0-or-1" role="doc-backlink">Comparison Operators Not a Shortcut for Producing 0 or 1</a></h3> Prior to Python 2.3, comparison operations returned 0 or 1 rather than True or False. Some code may have used this as a shortcut for producing zero or one in places where their boolean counterparts are not appropriate. For example: <div class="highlight-default notranslate"><div class="highlight"><pre>def identity(m=1): """Create and m-by-m identity matrix""" return [[i==j for i in range(m)] for j in range(m)] </pre></div> </div> In Python 2.2, a call to identity(2) would produce: <div class="highlight-default notranslate"><div class="highlight"><pre>[[1, 0], [0, 1]] </pre></div> </div> In Python 2.3, the same call would produce: <div class="highlight-default notranslate"><div class="highlight"><pre>[[True, False], [False, True]] </pre></div> </div> Since booleans are a subclass of integers, the matrix would continue to calculate normally, but it will not print as expected. The list comprehension should be changed to read: <div class="highlight-default notranslate"><div class="highlight"><pre>return [[int(i==j) for i in range(m)] for j in range(m)] </pre></div> </div> There are similar concerns when storing data to be used by other applications which may expect a number instead of True or False. </section> </section> <section id="modernization-procedures"> <h2><a class="toc-backref" href="#modernization-procedures" role="doc-backlink">Modernization Procedures</a></h2> Procedures are grouped by the Python version required to be able to take advantage of the modernization. <section id="python-2-4-or-later"> <h3><a class="toc-backref" href="#python-2-4-or-later" role="doc-backlink">Python 2.4 or Later</a></h3> <section id="inserting-and-popping-at-the-beginning-of-lists"> <h4><a class="toc-backref" href="#inserting-and-popping-at-the-beginning-of-lists" role="doc-backlink">Inserting and Popping at the Beginning of Lists</a></h4> Python’s lists are implemented to perform best with appends and pops on the right. Use of <code class="docutils literal notranslate">pop(0)</code> or <code class="docutils literal notranslate">insert(0, x)</code> triggers O(n) data movement for the entire list. To help address this need, Python 2.4 introduces a new container, <code class="docutils literal notranslate">collections.deque()</code> which has efficient append and pop operations on the both the left and right (the trade-off is much slower getitem/setitem access). The new container is especially helpful for implementing data queues: Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>c = list(data) --> c = collections.deque(data) c.pop(0) --> c.popleft() c.insert(0, x) --> c.appendleft() </pre></div> </div> Locating: <div class="highlight-default notranslate"><div class="highlight"><pre>grep pop(0 or grep insert(0 </pre></div> </div> </section> <section id="simplifying-custom-sorts"> <h4><a class="toc-backref" href="#simplifying-custom-sorts" role="doc-backlink">Simplifying Custom Sorts</a></h4> In Python 2.4, the <code class="docutils literal notranslate">sort</code> method for lists and the new <code class="docutils literal notranslate">sorted</code> built-in function both accept a <code class="docutils literal notranslate">key</code> function for computing sort keys. Unlike the <code class="docutils literal notranslate">cmp</code> function which gets applied to every comparison, the key function gets applied only once to each record. It is much faster than cmp and typically more readable while using less code. The key function also maintains the stability of the sort (records with the same key are left in their original order. Original code using a comparison function: <div class="highlight-default notranslate"><div class="highlight"><pre>names.sort(lambda x,y: cmp(x.lower(), y.lower())) </pre></div> </div> Alternative original code with explicit decoration: <div class="highlight-default notranslate"><div class="highlight"><pre>tempnames = [(n.lower(), n) for n in names] tempnames.sort() names = [original for decorated, original in tempnames] </pre></div> </div> Revised code using a key function: <div class="highlight-default notranslate"><div class="highlight"><pre>names.sort(key=str.lower) # case-insensitive sort </pre></div> </div> Locating: <code class="docutils literal notranslate">grep sort *.py</code> </section> <section id="replacing-common-uses-of-lambda"> <h4><a class="toc-backref" href="#replacing-common-uses-of-lambda" role="doc-backlink">Replacing Common Uses of Lambda</a></h4> In Python 2.4, the <code class="docutils literal notranslate">operator</code> module gained two new functions, itemgetter() and attrgetter() that can replace common uses of the <code class="docutils literal notranslate">lambda</code> keyword. The new functions run faster and are considered by some to improve readability. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>lambda r: r[2] --> itemgetter(2) lambda r: r.myattr --> attrgetter('myattr') </pre></div> </div> Typical contexts: <div class="highlight-default notranslate"><div class="highlight"><pre>sort(studentrecords, key=attrgetter('gpa')) # set a sort field map(attrgetter('lastname'), studentrecords) # extract a field </pre></div> </div> Locating: <code class="docutils literal notranslate">grep lambda *.py</code> </section> <section id="simplified-reverse-iteration"> <h4><a class="toc-backref" href="#simplified-reverse-iteration" role="doc-backlink">Simplified Reverse Iteration</a></h4> Python 2.4 introduced the <code class="docutils literal notranslate">reversed</code> builtin function for reverse iteration. The existing approaches to reverse iteration suffered from wordiness, performance issues (speed and memory consumption), and/or lack of clarity. A preferred style is to express the sequence in a forwards direction, apply <code class="docutils literal notranslate">reversed</code> to the result, and then loop over the resulting fast, memory friendly iterator. Original code expressed with half-open intervals: <div class="highlight-default notranslate"><div class="highlight"><pre>for i in range(n-1, -1, -1): print seqn[i] </pre></div> </div> Alternative original code reversed in multiple steps: <div class="highlight-default notranslate"><div class="highlight"><pre>rseqn = list(seqn) rseqn.reverse() for value in rseqn: print value </pre></div> </div> Alternative original code expressed with extending slicing: <div class="highlight-default notranslate"><div class="highlight"><pre>for value in seqn[::-1]: print value </pre></div> </div> Revised code using the <code class="docutils literal notranslate">reversed</code> function: <div class="highlight-default notranslate"><div class="highlight"><pre>for value in reversed(seqn): print value </pre></div> </div> </section> </section> <section id="python-2-3-or-later"> <h3><a class="toc-backref" href="#python-2-3-or-later" role="doc-backlink">Python 2.3 or Later</a></h3> <section id="testing-string-membership"> <h4><a class="toc-backref" href="#testing-string-membership" role="doc-backlink">Testing String Membership</a></h4> In Python 2.3, for <code class="docutils literal notranslate">string2 in string1</code>, the length restriction on <code class="docutils literal notranslate">string2</code> is lifted; it can now be a string of any length. When searching for a substring, where you don’t care about the position of the substring in the original string, using the <code class="docutils literal notranslate">in</code> operator makes the meaning clear. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>string1.find(string2) >= 0 --> string2 in string1 string1.find(string2) != -1 --> string2 in string1 </pre></div> </div> </section> <section id="replace-apply-with-a-direct-function-call"> <h4><a class="toc-backref" href="#replace-apply-with-a-direct-function-call" role="doc-backlink">Replace apply() with a Direct Function Call</a></h4> In Python 2.3, apply() was marked for Pending Deprecation because it was made obsolete by Python 1.6’s introduction of * and ** in function calls. Using a direct function call was always a little faster than apply() because it saved the lookup for the builtin. Now, apply() is even slower due to its use of the warnings module. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>apply(f, args, kwds) --> f(*args, **kwds) </pre></div> </div> Note: The Pending Deprecation was removed from apply() in Python 2.3.3 since it creates pain for people who need to maintain code that works with Python versions as far back as 1.5.2, where there was no alternative to apply(). The function remains deprecated, however. </section> </section> <section id="python-2-2-or-later"> <h3><a class="toc-backref" href="#python-2-2-or-later" role="doc-backlink">Python 2.2 or Later</a></h3> <section id="testing-dictionary-membership"> <h4><a class="toc-backref" href="#testing-dictionary-membership" role="doc-backlink">Testing Dictionary Membership</a></h4> For testing dictionary membership, use the ‘in’ keyword instead of the ‘has_key()’ method. The result is shorter and more readable. The style becomes consistent with tests for membership in lists. The result is slightly faster because <code class="docutils literal notranslate">has_key</code> requires an attribute search and uses a relatively expensive function call. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>if d.has_key(k): --> if k in d: </pre></div> </div> Contra-indications: <ol class="arabic"> <li>Some dictionary-like objects may not define a <code class="docutils literal notranslate">__contains__()</code> method:<div class="highlight-default notranslate"><div class="highlight"><pre>if dictlike.has_key(k) </pre></div> </div> </li> </ol> Locating: <code class="docutils literal notranslate">grep has_key</code> </section> <section id="looping-over-dictionaries"> <h4><a class="toc-backref" href="#looping-over-dictionaries" role="doc-backlink">Looping Over Dictionaries</a></h4> Use the new <code class="docutils literal notranslate">iter</code> methods for looping over dictionaries. The <code class="docutils literal notranslate">iter</code> methods are faster because they do not have to create a new list object with a complete copy of all of the keys, values, or items. Selecting only keys, values, or items (key/value pairs) as needed saves the time for creating throwaway object references and, in the case of items, saves a second hash look-up of the key. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>for key in d.keys(): --> for key in d: for value in d.values(): --> for value in d.itervalues(): for key, value in d.items(): --> for key, value in d.iteritems(): </pre></div> </div> Contra-indications: <ol class="arabic"> <li>If you need a list, do not change the return type:<div class="highlight-default notranslate"><div class="highlight"><pre>def getids(): return d.keys() </pre></div> </div> </li> <li>Some dictionary-like objects may not define <code class="docutils literal notranslate">iter</code> methods:<div class="highlight-default notranslate"><div class="highlight"><pre>for k in dictlike.keys(): </pre></div> </div> </li> <li>Iterators do not support slicing, sorting or other operations:<div class="highlight-default notranslate"><div class="highlight"><pre>k = d.keys(); j = k[:] </pre></div> </div> </li> <li>Dictionary iterators prohibit modifying the dictionary:<div class="highlight-default notranslate"><div class="highlight"><pre>for k in d.keys(): del[k] </pre></div> </div> </li> </ol> </section> <section id="stat-methods"> <h4><a class="toc-backref" href="#stat-methods" role="doc-backlink"><code class="docutils literal notranslate">stat</code> Methods</a></h4> Replace <code class="docutils literal notranslate">stat</code> constants or indices with new <code class="docutils literal notranslate">os.stat</code> attributes and methods. The <code class="docutils literal notranslate">os.stat</code> attributes and methods are not order-dependent and do not require an import of the <code class="docutils literal notranslate">stat</code> module. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>os.stat("foo")[stat.ST_MTIME] --> os.stat("foo").st_mtime os.stat("foo")[stat.ST_MTIME] --> os.path.getmtime("foo") </pre></div> </div> Locating: <code class="docutils literal notranslate">grep os.stat</code> or <code class="docutils literal notranslate">grep stat.S</code> </section> <section id="reduce-dependency-on-types-module"> <h4><a class="toc-backref" href="#reduce-dependency-on-types-module" role="doc-backlink">Reduce Dependency on <code class="docutils literal notranslate">types</code> Module</a></h4> The <code class="docutils literal notranslate">types</code> module is likely to be deprecated in the future. Use built-in constructor functions instead. They may be slightly faster. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>isinstance(v, types.IntType) --> isinstance(v, int) isinstance(s, types.StringTypes) --> isinstance(s, basestring) </pre></div> </div> Full use of this technique requires Python 2.3 or later (<code class="docutils literal notranslate">basestring</code> was introduced in Python 2.3), but Python 2.2 is sufficient for most uses. Locating: <code class="docutils literal notranslate">grep types *.py | grep import</code> </section> <section id="avoid-variable-names-that-clash-with-the-builtins-module"> <h4><a class="toc-backref" href="#avoid-variable-names-that-clash-with-the-builtins-module" role="doc-backlink">Avoid Variable Names that Clash with the <code class="docutils literal notranslate">__builtins__</code> Module</a></h4> In Python 2.2, new built-in types were added for <code class="docutils literal notranslate">dict</code> and <code class="docutils literal notranslate">file</code>. Scripts should avoid assigning variable names that mask those types. The same advice also applies to existing builtins like <code class="docutils literal notranslate">list</code>. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>file = open('myfile.txt') --> f = open('myfile.txt') dict = obj.__dict__ --> d = obj.__dict__ </pre></div> </div> Locating: <code class="docutils literal notranslate">grep 'file ' *.py</code> </section> </section> <section id="python-2-1-or-later"> <h3><a class="toc-backref" href="#python-2-1-or-later" role="doc-backlink">Python 2.1 or Later</a></h3> <section id="whrandom-module-deprecated"> <h4><a class="toc-backref" href="#whrandom-module-deprecated" role="doc-backlink"><code class="docutils literal notranslate">whrandom</code> Module Deprecated</a></h4> All random-related methods have been collected in one place, the <code class="docutils literal notranslate">random</code> module. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>import whrandom --> import random </pre></div> </div> Locating: <code class="docutils literal notranslate">grep whrandom</code> </section> </section> <section id="python-2-0-or-later"> <h3><a class="toc-backref" href="#python-2-0-or-later" role="doc-backlink">Python 2.0 or Later</a></h3> <section id="string-methods"> <h4><a class="toc-backref" href="#string-methods" role="doc-backlink">String Methods</a></h4> The string module is likely to be deprecated in the future. Use string methods instead. They’re faster too. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>import string ; string.method(s, ...) --> s.method(...) c in string.whitespace --> c.isspace() </pre></div> </div> Locating: <code class="docutils literal notranslate">grep string *.py | grep import</code> </section> <section id="startswith-and-endswith-string-methods"> <h4><a class="toc-backref" href="#startswith-and-endswith-string-methods" role="doc-backlink"><code class="docutils literal notranslate">startswith</code> and <code class="docutils literal notranslate">endswith</code> String Methods</a></h4> Use these string methods instead of slicing. No slice has to be created and there’s no risk of miscounting. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>"foobar"[:3] == "foo" --> "foobar".startswith("foo") "foobar"[-3:] == "bar" --> "foobar".endswith("bar") </pre></div> </div> </section> <section id="the-atexit-module"> <h4><a class="toc-backref" href="#the-atexit-module" role="doc-backlink">The <code class="docutils literal notranslate">atexit</code> Module</a></h4> The atexit module supports multiple functions to be executed upon program termination. Also, it supports parameterized functions. Unfortunately, its implementation conflicts with the sys.exitfunc attribute which only supports a single exit function. Code relying on sys.exitfunc may interfere with other modules (including library modules) that elect to use the newer and more versatile atexit module. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>sys.exitfunc = myfunc --> atexit.register(myfunc) </pre></div> </div> </section> </section> <section id="python-1-5-or-later"> <h3><a class="toc-backref" href="#python-1-5-or-later" role="doc-backlink">Python 1.5 or Later</a></h3> <section id="class-based-exceptions"> <h4><a class="toc-backref" href="#class-based-exceptions" role="doc-backlink">Class-Based Exceptions</a></h4> String exceptions are deprecated, so derive from the <code class="docutils literal notranslate">Exception</code> base class. Unlike the obsolete string exceptions, class exceptions all derive from another exception or the <code class="docutils literal notranslate">Exception</code> base class. This allows meaningful groupings of exceptions. It also allows an “<code class="docutils literal notranslate">except Exception</code>” clause to catch all exceptions. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>NewError = 'NewError' --> class NewError(Exception): pass </pre></div> </div> Locating: Use <a class="reference external" href="http://pychecker.sourceforge.net/">PyChecker</a>. </section> </section> <section id="all-python-versions"> <h3><a class="toc-backref" href="#all-python-versions" role="doc-backlink">All Python Versions</a></h3> <section id="testing-for-none"> <h4><a class="toc-backref" href="#testing-for-none" role="doc-backlink">Testing for <code class="docutils literal notranslate">None</code></a></h4> Since there is only one <code class="docutils literal notranslate">None</code> object, equality can be tested with identity. Identity tests are slightly faster than equality tests. Also, some object types may overload comparison, so equality testing may be much slower. Pattern: <div class="highlight-default notranslate"><div class="highlight"><pre>if v == None --> if v is None: if v != None --> if v is not None: </pre></div> </div> Locating: <code class="docutils literal notranslate">grep '== None'</code> or <code class="docutils literal notranslate">grep '!= None'</code> </section> </section> </section> <section id="copyright"> <h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2> This document has been placed in the public domain. </section> </section> <hr class="docutils" /> Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0290.rst">https://github.com/python/peps/blob/main/peps/pep-0290.rst</a> Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0290.rst">2025-02-01 08:59:27 GMT</a> </article> <nav id="pep-sidebar"> <h2>Contents</h2> <ul> <li><a class="reference internal" href="#abstract">Abstract</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#guidelines-for-new-entries">Guidelines for New Entries</a></li> <li><a class="reference internal" href="#migration-issues">Migration Issues</a><ul> <li><a class="reference internal" href="#comparison-operators-not-a-shortcut-for-producing-0-or-1">Comparison Operators Not a Shortcut for Producing 0 or 1</a></li> </ul> </li> <li><a class="reference internal" href="#modernization-procedures">Modernization Procedures</a><ul> <li><a class="reference internal" href="#python-2-4-or-later">Python 2.4 or Later</a><ul> <li><a class="reference internal" href="#inserting-and-popping-at-the-beginning-of-lists">Inserting and Popping at the Beginning of Lists</a></li> <li><a class="reference internal" href="#simplifying-custom-sorts">Simplifying Custom Sorts</a></li> <li><a class="reference internal" href="#replacing-common-uses-of-lambda">Replacing Common Uses of Lambda</a></li> <li><a class="reference internal" href="#simplified-reverse-iteration">Simplified Reverse Iteration</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-3-or-later">Python 2.3 or Later</a><ul> <li><a class="reference internal" href="#testing-string-membership">Testing String Membership</a></li> <li><a class="reference internal" href="#replace-apply-with-a-direct-function-call">Replace apply() with a Direct Function Call</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-2-or-later">Python 2.2 or Later</a><ul> <li><a class="reference internal" href="#testing-dictionary-membership">Testing Dictionary Membership</a></li> <li><a class="reference internal" href="#looping-over-dictionaries">Looping Over Dictionaries</a></li> <li><a class="reference internal" href="#stat-methods"><code class="docutils literal notranslate">stat</code> Methods</a></li> <li><a class="reference internal" href="#reduce-dependency-on-types-module">Reduce Dependency on <code class="docutils literal notranslate">types</code> Module</a></li> <li><a class="reference internal" href="#avoid-variable-names-that-clash-with-the-builtins-module">Avoid Variable Names that Clash with the <code class="docutils literal notranslate">__builtins__</code> Module</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-1-or-later">Python 2.1 or Later</a><ul> <li><a class="reference internal" href="#whrandom-module-deprecated"><code class="docutils literal notranslate">whrandom</code> Module Deprecated</a></li> </ul> </li> <li><a class="reference internal" href="#python-2-0-or-later">Python 2.0 or Later</a><ul> <li><a class="reference internal" href="#string-methods">String Methods</a></li> <li><a class="reference internal" href="#startswith-and-endswith-string-methods"><code class="docutils literal notranslate">startswith</code> and <code class="docutils literal notranslate">endswith</code> String Methods</a></li> <li><a class="reference internal" href="#the-atexit-module">The <code class="docutils literal notranslate">atexit</code> Module</a></li> </ul> </li> <li><a class="reference internal" href="#python-1-5-or-later">Python 1.5 or Later</a><ul> <li><a class="reference internal" href="#class-based-exceptions">Class-Based Exceptions</a></li> </ul> </li> <li><a class="reference internal" href="#all-python-versions">All Python Versions</a><ul> <li><a class="reference internal" href="#testing-for-none">Testing for <code class="docutils literal notranslate">None</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#copyright">Copyright</a></li> </ul> <a id="source" href="https://github.com/python/peps/blob/main/peps/pep-0290.rst">Page Source (GitHub)</a> </nav> </section> <script src="../_static/colour_scheme.js"></script> <script src="../_static/wrap_tables.js"></script> <script src="../_static/sticky_banner.js"></script> </body> </html>