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Language">Python</a> » </li> <li><a href="../pep-0000/">PEP Index</a> » </li> <li>PEP 266</li> </ul> <button id="colour-scheme-cycler" onClick="setColourScheme(nextColourScheme())"> <svg aria-hidden="true" class="colour-scheme-icon-when-auto"><use href="#svg-sun-half"></use></svg> <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 266 – Optimizing Global Variable/Attribute Access</h1> <dl class="rfc2822 field-list simple"> <dt class="field-odd">Author:</dt> <dd class="field-odd">Skip Montanaro <skip at pobox.com></dd> <dt class="field-even">Status:</dt> <dd class="field-even"><abbr title="Removed from consideration by sponsor or authors">Withdrawn</abbr></dd> <dt class="field-odd">Type:</dt> <dd class="field-odd"><abbr title="Normative PEP with a new feature for Python, implementation change for CPython or interoperability standard for the ecosystem">Standards Track</abbr></dd> <dt class="field-even">Created:</dt> <dd class="field-even">13-Aug-2001</dd> <dt class="field-odd">Python-Version:</dt> <dd class="field-odd">2.3</dd> <dt class="field-even">Post-History:</dt> <dd class="field-even"></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="#introduction">Introduction</a></li> <li><a class="reference internal" href="#proposed-change">Proposed Change</a></li> <li><a class="reference internal" href="#threads">Threads</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#questions">Questions</a><ul> <li><a class="reference internal" href="#what-about-threads-what-if-math-sin-changes-while-in-cache">What about threads? What if <code class="docutils literal notranslate">math.sin</code> changes while in cache?</a></li> </ul> </li> <li><a class="reference internal" href="#unresolved-issues">Unresolved Issues</a><ul> <li><a class="reference internal" href="#threading">Threading</a></li> <li><a class="reference internal" href="#nested-scopes">Nested Scopes</a></li> <li><a class="reference internal" href="#missing-attributes">Missing Attributes</a></li> <li><a class="reference internal" href="#who-does-the-dirty-work">Who does the dirty work?</a></li> </ul> </li> <li><a class="reference internal" href="#discussion">Discussion</a></li> <li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li> <li><a class="reference internal" href="#implementation">Implementation</a></li> <li><a class="reference internal" href="#performance">Performance</a></li> <li><a class="reference internal" href="#references">References</a></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> The bindings for most global variables and attributes of other modules typically never change during the execution of a Python program, but because of Python’s dynamic nature, code which accesses such global objects must run through a full lookup each time the object is needed. This PEP proposes a mechanism that allows code that accesses most global objects to treat them as local objects and places the burden of updating references on the code that changes the name bindings of such objects. </section> <section id="introduction"> <h2><a class="toc-backref" href="#introduction" role="doc-backlink">Introduction</a></h2> Consider the workhorse function <code class="docutils literal notranslate">sre_compile._compile</code>. It is the internal compilation function for the <code class="docutils literal notranslate">sre</code> module. It consists almost entirely of a loop over the elements of the pattern being compiled, comparing opcodes with known constant values and appending tokens to an output list. Most of the comparisons are with constants imported from the <code class="docutils literal notranslate">sre_constants</code> module. This means there are lots of <code class="docutils literal notranslate">LOAD_GLOBAL</code> bytecodes in the compiled output of this module. Just by reading the code it’s apparent that the author intended <code class="docutils literal notranslate">LITERAL</code>, <code class="docutils literal notranslate">NOT_LITERAL</code>, <code class="docutils literal notranslate">OPCODES</code> and many other symbols to be constants. Still, each time they are involved in an expression, they must be looked up anew. Most global accesses are actually to objects that are “almost constants”. This includes global variables in the current module as well as the attributes of other imported modules. Since they rarely change, it seems reasonable to place the burden of updating references to such objects on the code that changes the name bindings. If <code class="docutils literal notranslate">sre_constants.LITERAL</code> is changed to refer to another object, perhaps it would be worthwhile for the code that modifies the <code class="docutils literal notranslate">sre_constants</code> module dict to correct any active references to that object. By doing so, in many cases global variables and the attributes of many objects could be cached as local variables. If the bindings between the names given to the objects and the objects themselves changes rarely, the cost of keeping track of such objects should be low and the potential payoff fairly large. In an attempt to gauge the effect of this proposal, I modified the Pystone benchmark program included in the Python distribution to cache global functions. Its main function, <code class="docutils literal notranslate">Proc0</code>, makes calls to ten different functions inside its <code class="docutils literal notranslate">for</code> loop. In addition, <code class="docutils literal notranslate">Func2</code> calls <code class="docutils literal notranslate">Func1</code> repeatedly inside a loop. If local copies of these 11 global identifiers are made before the functions’ loops are entered, performance on this particular benchmark improves by about two percent (from 5561 pystones to 5685 on my laptop). It gives some indication that performance would be improved by caching most global variable access. Note also that the pystone benchmark makes essentially no accesses of global module attributes, an anticipated area of improvement for this PEP. </section> <section id="proposed-change"> <h2><a class="toc-backref" href="#proposed-change" role="doc-backlink">Proposed Change</a></h2> I propose that the Python virtual machine be modified to include <code class="docutils literal notranslate">TRACK_OBJECT</code> and <code class="docutils literal notranslate">UNTRACK_OBJECT</code> opcodes. <code class="docutils literal notranslate">TRACK_OBJECT</code> would associate a global name or attribute of a global name with a slot in the local variable array and perform an initial lookup of the associated object to fill in the slot with a valid value. The association it creates would be noted by the code responsible for changing the name-to-object binding to cause the associated local variable to be updated. The <code class="docutils literal notranslate">UNTRACK_OBJECT</code> opcode would delete any association between the name and the local variable slot. </section> <section id="threads"> <h2><a class="toc-backref" href="#threads" role="doc-backlink">Threads</a></h2> Operation of this code in threaded programs will be no different than in unthreaded programs. If you need to lock an object to access it, you would have had to do that before <code class="docutils literal notranslate">TRACK_OBJECT</code> would have been executed and retain that lock until after you stop using it. FIXME: I suspect I need more here. </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> Global variables and attributes rarely change. For example, once a function imports the math module, the binding between the name math and the module it refers to aren’t likely to change. Similarly, if the function that uses the <code class="docutils literal notranslate">math</code> module refers to its sin attribute, it’s unlikely to change. Still, every time the module wants to call the <code class="docutils literal notranslate">math.sin</code> function, it must first execute a pair of instructions: <div class="highlight-default notranslate"><div class="highlight"><pre>LOAD_GLOBAL math LOAD_ATTR sin </pre></div> </div> If the client module always assumed that <code class="docutils literal notranslate">math.sin</code> was a local constant and it was the responsibility of “external forces” outside the function to keep the reference correct, we might have code like this: <div class="highlight-default notranslate"><div class="highlight"><pre>TRACK_OBJECT math.sin ... LOAD_FAST math.sin ... UNTRACK_OBJECT math.sin </pre></div> </div> If the <code class="docutils literal notranslate">LOAD_FAST</code> was in a loop the payoff in reduced global loads and attribute lookups could be significant. This technique could, in theory, be applied to any global variable access or attribute lookup. Consider this code: <div class="highlight-default notranslate"><div class="highlight"><pre>l = [] for i in range(10): l.append(math.sin(i)) return l </pre></div> </div> Even though l is a local variable, you still pay the cost of loading <code class="docutils literal notranslate">l.append</code> ten times in the loop. The compiler (or an optimizer) could recognize that both <code class="docutils literal notranslate">math.sin</code> and <code class="docutils literal notranslate">l.append</code> are being called in the loop and decide to generate the tracked local code, avoiding it for the builtin <code class="docutils literal notranslate">range()</code> function because it’s only called once during loop setup. Performance issues related to accessing local variables make tracking <code class="docutils literal notranslate">l.append</code> less attractive than tracking globals such as <code class="docutils literal notranslate">math.sin</code>. According to a post to python-dev by Marc-Andre Lemburg <a class="footnote-reference brackets" href="#id4" id="id1">[1]</a>, <code class="docutils literal notranslate">LOAD_GLOBAL</code> opcodes account for over 7% of all instructions executed by the Python virtual machine. This can be a very expensive instruction, at least relative to a <code class="docutils literal notranslate">LOAD_FAST</code> instruction, which is a simple array index and requires no extra function calls by the virtual machine. I believe many <code class="docutils literal notranslate">LOAD_GLOBAL</code> instructions and <code class="docutils literal notranslate">LOAD_GLOBAL/LOAD_ATTR</code> pairs could be converted to <code class="docutils literal notranslate">LOAD_FAST</code> instructions. Code that uses global variables heavily often resorts to various tricks to avoid global variable and attribute lookup. The aforementioned <code class="docutils literal notranslate">sre_compile._compile</code> function caches the <code class="docutils literal notranslate">append</code> method of the growing output list. Many people commonly abuse functions’ default argument feature to cache global variable lookups. Both of these schemes are hackish and rarely address all the available opportunities for optimization. (For example, <code class="docutils literal notranslate">sre_compile._compile</code> does not cache the two globals that it uses most frequently: the builtin <code class="docutils literal notranslate">len</code> function and the global <code class="docutils literal notranslate">OPCODES</code> array that it imports from <code class="docutils literal notranslate">sre_constants.py</code>. </section> <section id="questions"> <h2><a class="toc-backref" href="#questions" role="doc-backlink">Questions</a></h2> <section id="what-about-threads-what-if-math-sin-changes-while-in-cache"> <h3><a class="toc-backref" href="#what-about-threads-what-if-math-sin-changes-while-in-cache" role="doc-backlink">What about threads? What if <code class="docutils literal notranslate">math.sin</code> changes while in cache?</a></h3> I believe the global interpreter lock will protect values from being corrupted. In any case, the situation would be no worse than it is today. If one thread modified <code class="docutils literal notranslate">math.sin</code> after another thread had already executed <code class="docutils literal notranslate">LOAD_GLOBAL math</code>, but before it executed <code class="docutils literal notranslate">LOAD_ATTR sin</code>, the client thread would see the old value of <code class="docutils literal notranslate">math.sin</code>. The idea is this. I use a multi-attribute load below as an example, not because it would happen very often, but because by demonstrating the recursive nature with an extra call hopefully it will become clearer what I have in mind. Suppose a function defined in module <code class="docutils literal notranslate">foo</code> wants to access <code class="docutils literal notranslate">spam.eggs.ham</code> and that <code class="docutils literal notranslate">spam</code> is a module imported at the module level in <code class="docutils literal notranslate">foo</code>: <div class="highlight-default notranslate"><div class="highlight"><pre>import spam ... def somefunc(): ... x = spam.eggs.ham </pre></div> </div> Upon entry to <code class="docutils literal notranslate">somefunc</code>, a <code class="docutils literal notranslate">TRACK_GLOBAL</code> instruction will be executed: <div class="highlight-default notranslate"><div class="highlight"><pre>TRACK_GLOBAL spam.eggs.ham n </pre></div> </div> spam.eggs.ham is a string literal stored in the function’s constants array. n is a fastlocals index. <code class="docutils literal notranslate">&fastlocals[n]</code> is a reference to slot n in the executing frame’s <code class="docutils literal notranslate">fastlocals</code> array, the location in which the spam.eggs.ham reference will be stored. Here’s what I envision happening: <ol class="arabic"> <li>The <code class="docutils literal notranslate">TRACK_GLOBAL</code> instruction locates the object referred to by the name spam and finds it in its module scope. It then executes a C function like:<div class="highlight-default notranslate"><div class="highlight"><pre>_PyObject_TrackName(m, "spam.eggs.ham", &fastlocals[n]) </pre></div> </div> where <code class="docutils literal notranslate">m</code> is the module object with an attribute <code class="docutils literal notranslate">spam</code>. </li> <li>The module object strips the leading spam. and stores the necessary information (eggs.ham and <code class="docutils literal notranslate">&fastlocals[n]</code>) in case its binding for the name eggs changes. It then locates the object referred to by the key eggs in its dict and recursively calls:<div class="highlight-default notranslate"><div class="highlight"><pre>_PyObject_TrackName(eggs, "eggs.ham", &fastlocals[n]) </pre></div> </div> </li> <li>The <code class="docutils literal notranslate">eggs</code> object strips the leading eggs., stores the (ham, &fastlocals[n]) info, locates the object in its namespace called <code class="docutils literal notranslate">ham</code> and calls <code class="docutils literal notranslate">_PyObject_TrackName</code> once again:<div class="highlight-default notranslate"><div class="highlight"><pre>_PyObject_TrackName(ham, "ham", &fastlocals[n]) </pre></div> </div> </li> <li>The <code class="docutils literal notranslate">ham</code> object strips the leading string (no “.” this time, but that’s a minor point), sees that the result is empty, then uses its own value (<code class="docutils literal notranslate">self</code>, probably) to update the location it was handed:<div class="highlight-default notranslate"><div class="highlight"><pre>Py_XDECREF(&fastlocals[n]); &fastlocals[n] = self; Py_INCREF(&fastlocals[n]); </pre></div> </div> At this point, each object involved in resolving <code class="docutils literal notranslate">spam.eggs.ham</code> knows which entry in its namespace needs to be tracked and what location to update if that name changes. Furthermore, if the one name it is tracking in its local storage changes, it can call <code class="docutils literal notranslate">_PyObject_TrackName</code> using the new object once the change has been made. At the bottom end of the food chain, the last object will always strip a name, see the empty string and know that its value should be stuffed into the location it’s been passed. When the object referred to by the dotted expression <code class="docutils literal notranslate">spam.eggs.ham</code> is going to go out of scope, an <code class="docutils literal notranslate">UNTRACK_GLOBAL spam.eggs.ham n</code> instruction is executed. It has the effect of deleting all the tracking information that <code class="docutils literal notranslate">TRACK_GLOBAL</code> established. The tracking operation may seem expensive, but recall that the objects being tracked are assumed to be “almost constant”, so the setup cost will be traded off against hopefully multiple local instead of global loads. For globals with attributes the tracking setup cost grows but is offset by avoiding the extra <code class="docutils literal notranslate">LOAD_ATTR</code> cost. The <code class="docutils literal notranslate">TRACK_GLOBAL</code> instruction needs to perform a <code class="docutils literal notranslate">PyDict_GetItemString</code> for the first name in the chain to determine where the top-level object resides. Each object in the chain has to store a string and an address somewhere, probably in a dict that uses storage locations as keys (e.g. the <code class="docutils literal notranslate">&fastlocals[n]</code>) and strings as values. (This dict could possibly be a central dict of dicts whose keys are object addresses instead of a per-object dict.) It shouldn’t be the other way around because multiple active frames may want to track <code class="docutils literal notranslate">spam.eggs.ham</code>, but only one frame will want to associate that name with one of its fast locals slots. </li> </ol> </section> </section> <section id="unresolved-issues"> <h2><a class="toc-backref" href="#unresolved-issues" role="doc-backlink">Unresolved Issues</a></h2> <section id="threading"> <h3><a class="toc-backref" href="#threading" role="doc-backlink">Threading</a></h3> What about this (dumb) code?: <div class="highlight-default notranslate"><div class="highlight"><pre>l = [] lock = threading.Lock() ... def fill_l():: for i in range(1000):: lock.acquire() l.append(math.sin(i)) lock.release() ... def consume_l():: while 1:: lock.acquire() if l:: elt = l.pop() lock.release() fiddle(elt) </pre></div> </div> It’s not clear from a static analysis of the code what the lock is protecting. (You can’t tell at compile-time that threads are even involved can you?) Would or should it affect attempts to track <code class="docutils literal notranslate">l.append</code> or <code class="docutils literal notranslate">math.sin</code> in the <code class="docutils literal notranslate">fill_l</code> function? If we annotate the code with mythical <code class="docutils literal notranslate">track_object</code> and <code class="docutils literal notranslate">untrack_object</code> builtins (I’m not proposing this, just illustrating where stuff would go!), we get: <div class="highlight-default notranslate"><div class="highlight"><pre>l = [] lock = threading.Lock() ... def fill_l():: track_object("l.append", append) track_object("math.sin", sin) for i in range(1000):: lock.acquire() append(sin(i)) lock.release() untrack_object("math.sin", sin) untrack_object("l.append", append) ... def consume_l():: while 1:: lock.acquire() if l:: elt = l.pop() lock.release() fiddle(elt) </pre></div> </div> Is that correct both with and without threads (or at least equally incorrect with and without threads)? </section> <section id="nested-scopes"> <h3><a class="toc-backref" href="#nested-scopes" role="doc-backlink">Nested Scopes</a></h3> The presence of nested scopes will affect where <code class="docutils literal notranslate">TRACK_GLOBAL</code> finds a global variable, but shouldn’t affect anything after that. (I think.) </section> <section id="missing-attributes"> <h3><a class="toc-backref" href="#missing-attributes" role="doc-backlink">Missing Attributes</a></h3> Suppose I am tracking the object referred to by <code class="docutils literal notranslate">spam.eggs.ham</code> and <code class="docutils literal notranslate">spam.eggs</code> is rebound to an object that does not have a <code class="docutils literal notranslate">ham</code> attribute. It’s clear this will be an <code class="docutils literal notranslate">AttributeError</code> if the programmer attempts to resolve <code class="docutils literal notranslate">spam.eggs.ham</code> in the current Python virtual machine, but suppose the programmer has anticipated this case: <div class="highlight-default notranslate"><div class="highlight"><pre>if hasattr(spam.eggs, "ham"): print spam.eggs.ham elif hasattr(spam.eggs, "bacon"): print spam.eggs.bacon else: print "what? no meat?" </pre></div> </div> You can’t raise an <code class="docutils literal notranslate">AttributeError</code> when the tracking information is recalculated. If it does not raise <code class="docutils literal notranslate">AttributeError</code> and instead lets the tracking stand, it may be setting the programmer up for a very subtle error. One solution to this problem would be to track the shortest possible root of each dotted expression the function refers to directly. In the above example, <code class="docutils literal notranslate">spam.eggs</code> would be tracked, but <code class="docutils literal notranslate">spam.eggs.ham</code> and <code class="docutils literal notranslate">spam.eggs.bacon</code> would not. </section> <section id="who-does-the-dirty-work"> <h3><a class="toc-backref" href="#who-does-the-dirty-work" role="doc-backlink">Who does the dirty work?</a></h3> In the Questions section I postulated the existence of a <code class="docutils literal notranslate">_PyObject_TrackName</code> function. While the API is fairly easy to specify, the implementation behind-the-scenes is not so obvious. A central dictionary could be used to track the name/location mappings, but it appears that all <code class="docutils literal notranslate">setattr</code> functions might need to be modified to accommodate this new functionality. If all types used the <code class="docutils literal notranslate">PyObject_GenericSetAttr</code> function to set attributes that would localize the update code somewhat. They don’t however (which is not too surprising), so it seems that all <code class="docutils literal notranslate">getattrfunc</code> and <code class="docutils literal notranslate">getattrofunc</code> functions will have to be updated. In addition, this would place an absolute requirement on C extension module authors to call some function when an attribute changes value (<code class="docutils literal notranslate">PyObject_TrackUpdate</code>?). Finally, it’s quite possible that some attributes will be set by side effect and not by any direct call to a <code class="docutils literal notranslate">setattr</code> method of some sort. Consider a device interface module that has an interrupt routine that copies the contents of a device register into a slot in the object’s <code class="docutils literal notranslate">struct</code> whenever it changes. In these situations, more extensive modifications would have to be made by the module author. To identify such situations at compile time would be impossible. I think an extra slot could be added to <code class="docutils literal notranslate">PyTypeObjects</code> to indicate if an object’s code is safe for global tracking. It would have a default value of 0 (<code class="docutils literal notranslate">Py_TRACKING_NOT_SAFE</code>). If an extension module author has implemented the necessary tracking support, that field could be initialized to 1 (<code class="docutils literal notranslate">Py_TRACKING_SAFE</code>). <code class="docutils literal notranslate">_PyObject_TrackName</code> could check that field and issue a warning if it is asked to track an object that the author has not explicitly said was safe for tracking. </section> </section> <section id="discussion"> <h2><a class="toc-backref" href="#discussion" role="doc-backlink">Discussion</a></h2> Jeremy Hylton has an alternate proposal on the table <a class="footnote-reference brackets" href="#id5" id="id2">[2]</a>. His proposal seeks to create a hybrid dictionary/list object for use in global name lookups that would make global variable access look more like local variable access. While there is no C code available to examine, the Python implementation given in his proposal still appears to require dictionary key lookup. It doesn’t appear that his proposal could speed local variable attribute lookup, which might be worthwhile in some situations if potential performance burdens could be addressed. </section> <section id="backwards-compatibility"> <h2><a class="toc-backref" href="#backwards-compatibility" role="doc-backlink">Backwards Compatibility</a></h2> I don’t believe there will be any serious issues of backward compatibility. Obviously, Python bytecode that contains <code class="docutils literal notranslate">TRACK_OBJECT</code> opcodes could not be executed by earlier versions of the interpreter, but breakage at the bytecode level is often assumed between versions. </section> <section id="implementation"> <h2><a class="toc-backref" href="#implementation" role="doc-backlink">Implementation</a></h2> TBD. This is where I need help. I believe there should be either a central name/location registry or the code that modifies object attributes should be modified, but I’m not sure the best way to go about this. If you look at the code that implements the <code class="docutils literal notranslate">STORE_GLOBAL</code> and <code class="docutils literal notranslate">STORE_ATTR</code> opcodes, it seems likely that some changes will be required to <code class="docutils literal notranslate">PyDict_SetItem</code> and <code class="docutils literal notranslate">PyObject_SetAttr</code> or their String variants. Ideally, there’d be a fairly central place to localize these changes. If you begin considering tracking attributes of local variables you get into issues of modifying <code class="docutils literal notranslate">STORE_FAST</code> as well, which could be a problem, since the name bindings for local variables are changed much more frequently. (I think an optimizer could avoid inserting the tracking code for the attributes for any local variables where the variable’s name binding changes.) </section> <section id="performance"> <h2><a class="toc-backref" href="#performance" role="doc-backlink">Performance</a></h2> I believe (though I have no code to prove it at this point), that implementing <code class="docutils literal notranslate">TRACK_OBJECT</code> will generally not be much more expensive than a single <code class="docutils literal notranslate">LOAD_GLOBAL</code> instruction or a <code class="docutils literal notranslate">LOAD_GLOBAL</code>/<code class="docutils literal notranslate">LOAD_ATTR</code> pair. An optimizer should be able to avoid converting <code class="docutils literal notranslate">LOAD_GLOBAL</code> and <code class="docutils literal notranslate">LOAD_GLOBAL</code>/<code class="docutils literal notranslate">LOAD_ATTR</code> to the new scheme unless the object access occurred within a loop. Further down the line, a register-oriented replacement for the current Python virtual machine <a class="footnote-reference brackets" href="#id6" id="id3">[3]</a> could conceivably eliminate most of the <code class="docutils literal notranslate">LOAD_FAST</code> instructions as well. The number of tracked objects should be relatively small. All active frames of all active threads could conceivably be tracking objects, but this seems small compared to the number of functions defined in a given application. </section> <section id="references"> <h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2> <aside class="footnote-list brackets"> <aside class="footnote brackets" id="id4" role="doc-footnote"> <dt class="label" id="id4">[<a href="#id1">1</a>]</dt> <dd><a class="reference external" href="https://mail.python.org/pipermail/python-dev/2000-July/007609.html">https://mail.python.org/pipermail/python-dev/2000-July/007609.html</a></aside> <aside class="footnote brackets" id="id5" role="doc-footnote"> <dt class="label" id="id5">[<a href="#id2">2</a>]</dt> <dd><a class="reference external" href="http://www.zope.org/Members/jeremy/CurrentAndFutureProjects/FastGlobalsPEP">http://www.zope.org/Members/jeremy/CurrentAndFutureProjects/FastGlobalsPEP</a></aside> <aside class="footnote brackets" id="id6" role="doc-footnote"> <dt class="label" id="id6">[<a href="#id3">3</a>]</dt> <dd><a class="reference external" href="http://www.musi-cal.com/~skip/python/rattlesnake20010813.tar.gz">http://www.musi-cal.com/~skip/python/rattlesnake20010813.tar.gz</a></aside> </aside> </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-0266.rst">https://github.com/python/peps/blob/main/peps/pep-0266.rst</a> Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0266.rst">2025-02-01 08:55:40 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="#introduction">Introduction</a></li> <li><a class="reference internal" href="#proposed-change">Proposed Change</a></li> <li><a class="reference internal" href="#threads">Threads</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#questions">Questions</a><ul> <li><a class="reference internal" href="#what-about-threads-what-if-math-sin-changes-while-in-cache">What about threads? What if <code class="docutils literal notranslate">math.sin</code> changes while in cache?</a></li> </ul> </li> <li><a class="reference internal" href="#unresolved-issues">Unresolved Issues</a><ul> <li><a class="reference internal" href="#threading">Threading</a></li> <li><a class="reference internal" href="#nested-scopes">Nested Scopes</a></li> <li><a class="reference internal" href="#missing-attributes">Missing Attributes</a></li> <li><a class="reference internal" href="#who-does-the-dirty-work">Who does the dirty work?</a></li> </ul> </li> <li><a class="reference internal" href="#discussion">Discussion</a></li> <li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li> <li><a class="reference internal" href="#implementation">Implementation</a></li> <li><a class="reference internal" href="#performance">Performance</a></li> <li><a class="reference internal" href="#references">References</a></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-0266.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>