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<li class="nav-item nav-item-0"><a href="../index.html">Cheetah3 - The Python-Powered Template Engine</a> »</li> - <li class="nav-item nav-item-1"><a href="../chep.html" accesskey="U">Cheetah Enhancement Proposals</a> »</li> - </ul> - </div> - <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> - <div class="sphinxsidebarwrapper"> - <h3><a href="../index.html">Table Of Contents</a></h3> - <ul> -<li><a class="reference internal" href="#">(#2) Conditionalized #import behavior</a><ul> -<li><a class="reference internal" href="#abstract">Abstract</a></li> -<li><a class="reference internal" href="#motivation">Motivation</a></li> -<li><a class="reference internal" href="#specification">Specification</a></li> -<li><a class="reference internal" href="#rationale">Rationale</a></li> -<li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li> -<li><a class="reference internal" href="#reference-implementation">Reference Implementation</a></li> -<li><a class="reference internal" href="#copyright">Copyright</a></li> -</ul> -</li> -</ul> - 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<div class="bodywrapper"> - <div class="body" role="main"> - - <div class="section" id="conditionalized-import-behavior"> -<h1>(#2) Conditionalized #import behavior<a class="headerlink" href="#conditionalized-import-behavior" title="Permalink to this headline">¶</a></h1> -<table class="docutils field-list" frame="void" rules="none"> -<col class="field-name" /> -<col class="field-body" /> -<tbody valign="top"> -<tr class="field-odd field"><th class="field-name">CHEP:</th><td class="field-body">2</td> -</tr> -<tr class="field-even field"><th class="field-name">Title:</th><td class="field-body">Conditionalized #import behavior</td> -</tr> -<tr class="field-odd field"><th class="field-name">Version:</th><td class="field-body">1</td> -</tr> -<tr class="field-even field"><th class="field-name">Author:</th><td class="field-body">R Tyler Ballance <tyler at slide.com></td> -</tr> -<tr class="field-odd field"><th class="field-name">Status:</th><td class="field-body">Draft</td> -</tr> -<tr class="field-even field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td> -</tr> -<tr class="field-odd field"><th class="field-name">Content-Type:</th><td class="field-body">text/x-rst</td> -</tr> -<tr class="field-even field"><th class="field-name">Created:</th><td class="field-body">07-Jun-2009</td> -</tr> -</tbody> -</table> -<hr class="docutils" /> -<div class="section" id="abstract"> -<h2>Abstract<a class="headerlink" href="#abstract" title="Permalink to this headline">¶</a></h2> -<p>This CHEP proposes an update to the way the #import and #from -directives are handled such that locally scoped imports and -module-level imports are handled appropriately.</p> -</div> -<div class="section" id="motivation"> -<h2>Motivation<a class="headerlink" href="#motivation" title="Permalink to this headline">¶</a></h2> -<p>Currently Cheetah (v2.2.1) provides two different, but mutually exclusive, -means of importing Python modules with the #from/#import directives. The -“traditional” handling for #from/#import (hereafter referred to as “module imports”) -is that the generated import statements shall all be relocated to -the top of the generated module’s source code, i.e.</p> -<div class="highlight-default"><div class="highlight"><pre><span></span>#import cjson - -Hello $cjson.encode([1, 2, 3]) -</pre></div> -</div> -<p>Will result in generated module code along the lines of:</p> -<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">cjson</span> - -<span class="k">class</span> <span class="nc">Foo</span><span class="p">(</span><span class="n">Template</span><span class="p">):</span> - <span class="k">def</span> <span class="nf">writeBody</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> - <span class="n">write</span><span class="p">(</span><span class="s1">'Hello '</span><span class="p">)</span> - <span class="n">write</span><span class="p">(</span><span class="n">cjson</span><span class="o">.</span><span class="n">encode</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]))</span> -</pre></div> -</div> -<p>Also currently in Cheetah is the ability to switch off this -behavior and enable location specific #from/#import handling -(hereafter referred to as “function imports”) in the generated -code, with this block of Cheetah for example:</p> -<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1">#def aFunction(arg)</span> - <span class="c1">#try</span> - <span class="c1">#from hashlib import md5</span> - <span class="c1">#except ImportError</span> - <span class="c1">#from md5 import md5</span> - <span class="c1">#end try</span> - <span class="c1">#return $md5.new(arg).hexdigest()</span> -<span class="c1">#end def</span> -</pre></div> -</div> -<p>Will result in code generated with everything in -place such that the Python looks something like:</p> -<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Foo</span><span class="p">(</span><span class="n">Template</span><span class="p">):</span> - <span class="k">def</span> <span class="nf">aFunction</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span> - <span class="k">try</span><span class="p">:</span> - <span class="kn">from</span> <span class="nn">hashlib</span> <span class="k">import</span> <span class="n">md5</span> - <span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span> - <span class="kn">from</span> <span class="nn">md5</span> <span class="k">import</span> <span class="n">md5</span> - <span class="k">return</span> <span class="n">md5</span><span class="o">.</span><span class="n">new</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span> -</pre></div> -</div> -<p>These two approaches to handling the #from/#import directives -are both beneficial for different situations but currently they -are handled in mutually exclusive code paths and in mutually -exclusive fashions.</p> -</div> -<div class="section" id="specification"> -<h2>Specification<a class="headerlink" href="#specification" title="Permalink to this headline">¶</a></h2> -<p>The change in #from/#import behavior and how these directives -are handled is all based on context of their use, making the -#from/#import handling “intelligent”. For module imports, the -“traditional” handling of the #from/#import directives will -still apply. Whereas function imports will result in inline -generated import code.</p> -<p>The basic premise of the change proposed by this document is -that all #from/#import directives contained within a #def/#end def -closure will result in import statements contained within that -function block whereas everywhere else the statements will be relocated -to the top of the generated module code (i.e. the module import)</p> -</div> -<div class="section" id="rationale"> -<h2>Rationale<a class="headerlink" href="#rationale" title="Permalink to this headline">¶</a></h2> -<p>The concept of the “function import” was introduced in Cheetah v2.1.0 -and quickly retrofitted to “live” behind a compiler setting due to the -regressions with older templates or templates that were designed to utilize -module imports (through heavy #block/#end block use, etc). Through discussion -with Tavis Rudd, this middle ground between the two styles of importing was -concluded to be the most reasonable solution to providing “pythonic” import -functionality (i.e. “function import” also known as “inline imports”) while -still providing the ability to have #from/#import directives declared at the -module scope within the template (within the Cheetah templates, markup and most -directives declared within the module scope are placed inside the default method).</p> -</div> -<div class="section" id="backwards-compatibility"> -<h2>Backwards Compatibility<a class="headerlink" href="#backwards-compatibility" title="Permalink to this headline">¶</a></h2> -<p>Changes proposed in this document should be <em>mostly</em> backwards -compatible with current versions of Cheetah, Any unforeseen issues -could arise from the use of #from/#import inside of a function -expecting those symbols to be available outside of the function -that they’re declared in.</p> -</div> -<div class="section" id="reference-implementation"> -<h2>Reference Implementation<a class="headerlink" href="#reference-implementation" title="Permalink to this headline">¶</a></h2> -<p><em>still in development</em></p> -</div> -<div class="section" id="copyright"> -<h2>Copyright<a class="headerlink" href="#copyright" title="Permalink to this headline">¶</a></h2> -<p>This document has been placed in the public domain.</p> -</div> -</div> - - - </div> - </div> - </div> - <div class="clearer"></div> - </div> - <div class="related" role="navigation" aria-label="related navigation"> - <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="3_super.html" title="(#3) Exposing of super() and self via Template searchList" - >next</a> |</li> - <li class="right" > - <a href="1_chep.html" title="(#1) CHEP Purpose and Guidelines" - >previous</a> |</li> - <li class="nav-item nav-item-0"><a href="../index.html">Cheetah3 - The Python-Powered Template Engine</a> »</li> - <li class="nav-item nav-item-1"><a href="../chep.html" >Cheetah Enhancement Proposals</a> »</li> - </ul> - </div> - <div class="footer" role="contentinfo"> - © Copyright 2017, Oleg Broytman; 2009-2012, R. 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