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<div class="section" id="maintainer-reference">
<h1>Maintainer Reference<a class="headerlink" href="#maintainer-reference" title="Permalink to this headline">¶</a></h1>
<div class="section" id="the-api">
<h2>The <a class="reference external" href="api/index.html">API</a><a class="headerlink" href="#the-api" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference external" href="api/index.html">API</a> for PyXB was generated using <a class="reference external" href="http://epydoc.sourceforge.net/">Epydoc</a>. Most of the public API is commented,
though not all docstrings have been updated to use Epydoc syntax.</p>
</div>
<div class="section" id="coding-practices">
<h2>Coding Practices<a class="headerlink" href="#coding-practices" title="Permalink to this headline">¶</a></h2>
<p>The practices described herein are <em>intended</em> to be used, but evolved over
time, and not all are followed in every situation.</p>
<div class="section" id="style">
<h3>Style<a class="headerlink" href="#style" title="Permalink to this headline">¶</a></h3>
<p>PyXB follows generally uses a coding style consistent with those described
in the Python coding standard in <span class="target" id="index-1"></span><a class="reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a>. Specific exceptions are listed
below.</p>
<div class="section" id="whitespace">
<h4>Whitespace<a class="headerlink" href="#whitespace" title="Permalink to this headline">¶</a></h4>
<p>The pet peeves of PyXB’s maintainer differ from the <a class="reference external" href="http://en.wikipedia.org/wiki/Guido_van_Rossum">BDFL</a>‘s when it comes to
whitespace. Spaces are used around operators to reveal precedence
assumptions, and sometimes around parenthesis to distinguish tuple value
boundaries:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">hypot2</span> <span class="o">=</span> <span class="n">x</span><span class="o">*</span><span class="n">x</span> <span class="o">+</span> <span class="n">y</span><span class="o">*</span><span class="n">y</span>
<span class="n">pair_of_pairs</span> <span class="o">=</span> <span class="p">(</span> <span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">),</span> <span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="n">c</span><span class="p">)</span> <span class="p">)</span>
</pre></div>
</div>
<p>Definitions of methods and classes always use a space before the
parenthesis; invocations never do:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">declaration</span> <span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">recurse</span><span class="o">=</span><span class="bp">False</span><span class="p">):</span>
<span class="k">if</span> <span class="n">recurse</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">declaration</span><span class="p">(</span><span class="bp">False</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="naming">
<span id="identifier-naming"></span><h4>Naming<a class="headerlink" href="#naming" title="Permalink to this headline">¶</a></h4>
<p>PyXB heavily uses a single leading underscore as an indication of
protected/friend status, as suggested in <span class="target" id="index-2"></span><a class="reference external" href="http://www.python.org/dev/peps/pep-0008"><strong>PEP 8</strong></a>. Wherever possible,
double leading underscores are used to hide class member fields, restricting
access to them through protected or public accessor methods.</p>
<p>Class members that are specifically <em>class</em> (as opposed to <em>instance</em>)
members begin with a capital letter.</p>
<p>An underscore is used to separate the descriptive class or function name
from a suffix that indicates its use. Standard suffixes are:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">mixin</span></tt> : A class that does not stand alone, but is a superclass of one
or more classes</li>
<li><tt class="docutils literal"><span class="pre">csc</span></tt> : A method that uses <a class="reference internal" href="#coding-csc"><em>cooperative super calling</em></a></li>
<li><tt class="docutils literal"><span class="pre">vx</span></tt>, <tt class="docutils literal"><span class="pre">vb</span></tt> : An indication that the method is expected to be
overridden in a subclass.</li>
</ul>
</div>
</div>
<div class="section" id="exceptions">
<h3>Exceptions<a class="headerlink" href="#exceptions" title="Permalink to this headline">¶</a></h3>
<p>PyXB provides a <a class="reference external" href="api/pyxb.exceptions_-module.html">standard exception hierarchy</a> that extends the one built into Python.</p>
<p>Where an execution branch has been identified that requires behavior that
has not yet been implemented, raise an <a class="reference external" href="api/pyxb.exceptions_.IncompleteImplementationError-class.html">IncompleteImplementationError</a>.</p>
<p>Where the system detects that a precondition is not satisfied, processing
must stop. If the precondition failure is due to improper use of the PyXB
internal or public API, a <a class="reference external" href="api/pyxb.exceptions_.LogicError-class.html">LogicError</a> should be
raised. If the precondition failure is due to invalid input from the
schema, a <a class="reference external" href="api/pyxb.exceptions_.SchemaValidationError-class.html">SchemaValidationError</a> should be raised.</p>
<p>If the precondition is inexplicably false, Python’s <tt class="docutils literal"><span class="pre">assert</span></tt> functionality
may be used. Use of <tt class="docutils literal"><span class="pre">assert</span></tt> should be rare, and only in places that are
guaranteed to be exercised during the course of testing.</p>
<p>The exception behavior of methods SHOULD be documented. Documentation of
asserts is not required.</p>
</div>
<div class="section" id="annotations">
<h3>Annotations<a class="headerlink" href="#annotations" title="Permalink to this headline">¶</a></h3>
<p>Use decorators (<span class="target" id="index-3"></span><a class="reference external" href="http://www.python.org/dev/peps/pep-0318"><strong>PEP 318</strong></a>) to mark class methods. Note that this restricts
us to Python 2.4 or later. Sigh with disappointment and move on.</p>
</div>
<div class="section" id="documentation">
<h3>Documentation<a class="headerlink" href="#documentation" title="Permalink to this headline">¶</a></h3>
<p>Use the <a class="reference external" href="http://epydoc.sourceforge.net/manual-epytext.html">Epytext Markup Language</a> for all public and
implementation-shared methods and classes. (Formerly, this was “Use
docstrings <span class="target" id="index-4"></span><a class="reference external" href="http://www.python.org/dev/peps/pep-0257"><strong>PEP 257</strong></a>“. Documentation in only a few modules has been
converted.)</p>
</div>
<div class="section" id="comments">
<h3>Comments<a class="headerlink" href="#comments" title="Permalink to this headline">¶</a></h3>
<p>Use comments copiously. Do not duplicate detailed information from
standards, but do include pertinent summaries and a reference to the section
in which the details can be found. The casual reader should not be forced
to open the standard to figure out what the coder intended to accomplish.</p>
</div>
<div class="section" id="terminology">
<h3>Terminology<a class="headerlink" href="#terminology" title="Permalink to this headline">¶</a></h3>
<p>The term “attribute” has different meanings in Python and XML.</p>
<p>tag : Refers to the text that opens an XML element</p>
<p>instance : [as an adjective] Refers to a characteristic of an instance of a
Python class.</p>
<p>class : [as an adjective] Refers to a characteristic of a Python class
itself, shared among all instances.</p>
<p>field : Refers to a named attribute of a Python object (class). When the
attribute holds a value, it is an “instance (class) variable” or “instance
(class) field”. When it holds a reference to an invokable object, it is an
“instance (class) method”.</p>
</div>
<div class="section" id="use-of-new-style-classes">
<h3>Use of new-style classes<a class="headerlink" href="#use-of-new-style-classes" title="Permalink to this headline">¶</a></h3>
<p>Too many things, such as clean hooking into the pickling system, require the
use of <a class="reference external" href="http://www.geocities.com/foetsch/python/new_style_classes.htm">new-style classes</a>.
Namespaces, schema components, and types (simple and complex) all use
new-style classes.</p>
<p>For this to work properly, if you implement an <tt class="docutils literal"><span class="pre">__init__</span></tt> method, it must take
arbitrary args and keywords, invoke <tt class="docutils literal"><span class="pre">super(Class,</span> <span class="pre">self).__init__(*args,**kw)</span></tt>,
and extract any arguments it needs from the keywords. If you do not need to
do anything in the init method, leave it out. See
<a class="reference external" href="http://fuhm.net/super-harmful/">this commentary</a> for a detailed
description of the intricacies of <tt class="docutils literal"><span class="pre">super</span></tt>.</p>
</div>
<div class="section" id="inheritance">
<h3>Inheritance<a class="headerlink" href="#inheritance" title="Permalink to this headline">¶</a></h3>
<div class="section" id="mix-in-classes">
<span id="mixins"></span><h4>Mix-in classes<a class="headerlink" href="#mix-in-classes" title="Permalink to this headline">¶</a></h4>
<p>PyXB makes heavy use of multiple inheritance through <a class="reference external" href="http://en.wikipedia.org/wiki/Mixin">mix-in classes</a>. If there are constraints on where
the mix-in must appear in the method resolution order (mro), note that
clearly in the mix-in documentation.</p>
</div>
<div class="section" id="invoking-superclass-instances">
<span id="coding-csc"></span><h4>Invoking Superclass Instances<a class="headerlink" href="#invoking-superclass-instances" title="Permalink to this headline">¶</a></h4>
<p><a class="reference external" href="http://www.geocities.com/foetsch/python/new_style_classes.htm#super">Cooperative super calling</a> is a
pattern where a class may inherit multiple implementations of the same
method, and want to call all of them. Normally this is done by invoking the
parent class implementation before or after the subclass implementation. In
non-trivial inheritance hierarchies (as result from using many mix-ins),
it’s not obvious who the next parent to call is, so the Python <tt class="docutils literal"><span class="pre">super</span></tt>
function is used. However, at some point a class will be reached that has
no more definitions for the called method, and attempting to invoke one
would produce an <tt class="docutils literal"><span class="pre">AttributeError</span></tt>.</p>
<p>Use the following idiom to conditionally invoke superclass methods when you
are not sure the superclass has such a method.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">method_csc</span> <span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">):</span>
<span class="n">super_fn</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="nb">super</span><span class="p">(</span><span class="n">ThisClass</span><span class="p">,</span> <span class="bp">self</span><span class="p">),</span> <span class="s">'method_csc'</span><span class="p">,</span> <span class="k">lambda</span> <span class="o">*</span><span class="n">a</span><span class="p">,</span><span class="o">**</span><span class="n">kw</span><span class="p">:</span> <span class="bp">self</span><span class="p">)</span>
<span class="k">return</span> <span class="n">super_fn</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">)</span>
</pre></div>
</div>
<p>Note the use of the <tt class="docutils literal"><span class="pre">_csc</span></tt> suffix to highlight that this method uses
cooperative super calling.</p>
</div>
<div class="section" id="class-variables-at-multiple-levels">
<h4>Class Variables At Multiple Levels<a class="headerlink" href="#class-variables-at-multiple-levels" title="Permalink to this headline">¶</a></h4>
<p>There are several cases where we want to store information in a class, but
allow subclasses (not instances) to override it. An example is in the
<a class="reference external" href="api/pyxb.binding.basis.simpleTypeDefinition-class.html">simpleTypeDefinition</a> hierarchy where each class
maintains a set of <a class="reference external" href="api/pyxb.binding.facets.ConstrainingFacet-class.html">ConstrainingFacet</a> instances
that are available for constraining values of the class. In many cases, a
subclass will not change the set of facets that affect instances, so we want
to be able to inherit the parent class map; but in other cases we may need
to add constraints that only affect the new class and its descendents.</p>
<p>This sort of thing is supported by implementing a private class method in
the base class which combines the dynamically-determined actual class name
with a constant identifier and uses <tt class="docutils literal"><span class="pre">getattr</span></tt> and <tt class="docutils literal"><span class="pre">setattr</span></tt> to access
the class-specific value.</p>
<p>Type declarations may extend a type of the same name in a different
namespace. If they do so, their binding classes will likely have the same
name, but in different modules, while also inheriting (in exactly the
situation where we want different values). For this reason, the constructed
attribute name should also incorporate the module or namespace, something
normally not done with the double-underscore feature of Python.</p>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">Maintainer Reference</a><ul>
<li><a class="reference external" href="#the-api">The API</a></li>
<li><a class="reference external" href="#coding-practices">Coding Practices</a><ul>
<li><a class="reference external" href="#style">Style</a><ul>
<li><a class="reference external" href="#whitespace">Whitespace</a></li>
<li><a class="reference external" href="#naming">Naming</a></li>
</ul>
</li>
<li><a class="reference external" href="#exceptions">Exceptions</a></li>
<li><a class="reference external" href="#annotations">Annotations</a></li>
<li><a class="reference external" href="#documentation">Documentation</a></li>
<li><a class="reference external" href="#comments">Comments</a></li>
<li><a class="reference external" href="#terminology">Terminology</a></li>
<li><a class="reference external" href="#use-of-new-style-classes">Use of new-style classes</a></li>
<li><a class="reference external" href="#inheritance">Inheritance</a><ul>
<li><a class="reference external" href="#mix-in-classes">Mix-in classes</a></li>
<li><a class="reference external" href="#invoking-superclass-instances">Invoking Superclass Instances</a></li>
<li><a class="reference external" href="#class-variables-at-multiple-levels">Class Variables At Multiple Levels</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
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