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<section id="networkx-utils-decorators-argmap">
<h1>networkx.utils.decorators.argmap<a class="headerlink" href="#networkx-utils-decorators-argmap" title="Permalink to this heading">#</a></h1>
<dl class="py class">
<dt class="sig sig-object py" id="networkx.utils.decorators.argmap">
<em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">argmap</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">func</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">try_finally</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="../../_modules/networkx/utils/decorators.html#argmap"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#networkx.utils.decorators.argmap" title="Permalink to this definition">#</a></dt>
<dd><p>A decorator to apply a map to arguments before calling the function</p>
<p>This class provides a decorator that maps (transforms) arguments of the function
before the function is called. Thus for example, we have similar code
in many functions to determine whether an argument is the number of nodes
to be created, or a list of nodes to be handled. The decorator provides
the code to accept either – transforming the indicated argument into a
list of nodes before the actual function is called.</p>
<p>This decorator class allows us to process single or multiple arguments.
The arguments to be processed can be specified by string, naming the argument,
or by index, specifying the item in the args list.</p>
<dl class="field-list">
<dt class="field-odd">Parameters<span class="colon">:</span></dt>
<dd class="field-odd"><dl>
<dt><strong>func</strong><span class="classifier">callable</span></dt><dd><p>The function to apply to arguments</p>
</dd>
<dt><strong>*args</strong><span class="classifier">iterable of (int, str or tuple)</span></dt><dd><p>A list of parameters, specified either as strings (their names), ints
(numerical indices) or tuples, which may contain ints, strings, and
(recursively) tuples. Each indicates which parameters the decorator
should map. Tuples indicate that the map function takes (and returns)
multiple parameters in the same order and nested structure as indicated
here.</p>
</dd>
<dt><strong>try_finally</strong><span class="classifier">bool (default: False)</span></dt><dd><p>When True, wrap the function call in a try-finally block with code
for the finally block created by <code class="xref py py-obj docutils literal notranslate"><span class="pre">func</span></code>. This is used when the map
function constructs an object (like a file handle) that requires
post-processing (like closing).</p>
<p>Note: try_finally decorators cannot be used to decorate generator
functions.</p>
</dd>
</dl>
</dd>
</dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference internal" href="networkx.utils.decorators.not_implemented_for.html#networkx.utils.decorators.not_implemented_for" title="networkx.utils.decorators.not_implemented_for"><code class="xref py py-obj docutils literal notranslate"><span class="pre">not_implemented_for</span></code></a></dt><dd></dd>
<dt><a class="reference internal" href="networkx.utils.decorators.open_file.html#networkx.utils.decorators.open_file" title="networkx.utils.decorators.open_file"><code class="xref py py-obj docutils literal notranslate"><span class="pre">open_file</span></code></a></dt><dd></dd>
<dt><a class="reference internal" href="networkx.utils.decorators.nodes_or_number.html#networkx.utils.decorators.nodes_or_number" title="networkx.utils.decorators.nodes_or_number"><code class="xref py py-obj docutils literal notranslate"><span class="pre">nodes_or_number</span></code></a></dt><dd></dd>
<dt><code class="xref py py-obj docutils literal notranslate"><span class="pre">random_state</span></code></dt><dd></dd>
<dt><a class="reference internal" href="networkx.utils.decorators.py_random_state.html#networkx.utils.decorators.py_random_state" title="networkx.utils.decorators.py_random_state"><code class="xref py py-obj docutils literal notranslate"><span class="pre">py_random_state</span></code></a></dt><dd></dd>
<dt><code class="xref py py-obj docutils literal notranslate"><span class="pre">networkx.community.quality.require_partition</span></code></dt><dd></dd>
<dt><code class="xref py py-obj docutils literal notranslate"><span class="pre">require_partition</span></code></dt><dd></dd>
</dl>
</div>
<p class="rubric">Notes</p>
<p>An object of this class is callable and intended to be used when
defining a decorator. Generally, a decorator takes a function as input
and constructs a function as output. Specifically, an <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> object
returns the input function decorated/wrapped so that specified arguments
are mapped (transformed) to new values before the decorated function is called.</p>
<p>As an overview, the argmap object returns a new function with all the
dunder values of the original function (like <code class="xref py py-obj docutils literal notranslate"><span class="pre">__doc__</span></code>, <a class="reference external" href="https://docs.python.org/3/reference/import.html#name__" title="(in Python v3.11)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">__name__</span></code></a>, etc).
Code for this decorated function is built based on the original function’s
signature. It starts by mapping the input arguments to potentially new
values. Then it calls the decorated function with these new values in place
of the indicated arguments that have been mapped. The return value of the
original function is then returned. This new function is the function that
is actually called by the user.</p>
<dl>
<dt>Three additional features are provided.</dt><dd><p>1) The code is lazily compiled. That is, the new function is returned
as an object without the code compiled, but with all information
needed so it can be compiled upon it’s first invocation. This saves
time on import at the cost of additional time on the first call of
the function. Subsequent calls are then just as fast as normal.</p>
<p>2) If the “try_finally” keyword-only argument is True, a try block
follows each mapped argument, matched on the other side of the wrapped
call, by a finally block closing that mapping. We expect func to return
a 2-tuple: the mapped value and a function to be called in the finally
clause. This feature was included so the <a class="reference internal" href="networkx.utils.decorators.open_file.html#networkx.utils.decorators.open_file" title="networkx.utils.decorators.open_file"><code class="xref py py-obj docutils literal notranslate"><span class="pre">open_file</span></code></a> decorator could
provide a file handle to the decorated function and close the file handle
after the function call. It even keeps track of whether to close the file
handle or not based on whether it had to open the file or the input was
already open. So, the decorated function does not need to include any
code to open or close files.</p>
<p>3) The maps applied can process multiple arguments. For example,
you could swap two arguments using a mapping, or transform
them to their sum and their difference. This was included to allow
a decorator in the <code class="xref py py-obj docutils literal notranslate"><span class="pre">quality.py</span></code> module that checks that an input
<code class="xref py py-obj docutils literal notranslate"><span class="pre">partition</span></code> is a valid partition of the nodes of the input graph <code class="xref py py-obj docutils literal notranslate"><span class="pre">G</span></code>.
In this example, the map has inputs <code class="xref py py-obj docutils literal notranslate"><span class="pre">(G,</span> <span class="pre">partition)</span></code>. After checking
for a valid partition, the map either raises an exception or leaves
the inputs unchanged. Thus many functions that make this check can
use the decorator rather than copy the checking code into each function.
More complicated nested argument structures are described below.</p>
</dd>
</dl>
<p>The remaining notes describe the code structure and methods for this
class in broad terms to aid in understanding how to use it.</p>
<p>Instantiating an <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> object simply stores the mapping function and
the input identifiers of which arguments to map. The resulting decorator
is ready to use this map to decorate any function. Calling that object
(<code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap.__call__</span></code>, but usually done via <code class="xref py py-obj docutils literal notranslate"><span class="pre">@my_decorator</span></code>) a lazily
compiled thin wrapper of the decorated function is constructed,
wrapped with the necessary function dunder attributes like <code class="xref py py-obj docutils literal notranslate"><span class="pre">__doc__</span></code>
and <a class="reference external" href="https://docs.python.org/3/reference/import.html#name__" title="(in Python v3.11)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">__name__</span></code></a>. That thinly wrapped function is returned as the
decorated function. When that decorated function is called, the thin
wrapper of code calls <code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap._lazy_compile</span></code> which compiles the decorated
function (using <a class="reference internal" href="generated/networkx.utils.decorators.argmap.compile.html#networkx.utils.decorators.argmap.compile" title="networkx.utils.decorators.argmap.compile"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap.compile</span></code></a>) and replaces the code of the thin
wrapper with the newly compiled code. This saves the compilation step
every import of networkx, at the cost of compiling upon the first call
to the decorated function.</p>
<p>When the decorated function is compiled, the code is recursively assembled
using the <a class="reference internal" href="generated/networkx.utils.decorators.argmap.assemble.html#networkx.utils.decorators.argmap.assemble" title="networkx.utils.decorators.argmap.assemble"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap.assemble</span></code></a> method. The recursive nature is needed in
case of nested decorators. The result of the assembly is a number of
useful objects.</p>
<blockquote>
<div><dl>
<dt>sig<span class="classifier">the function signature of the original decorated function as</span></dt><dd><p>constructed by <a class="reference internal" href="generated/networkx.utils.decorators.argmap.signature.html#networkx.utils.decorators.argmap.signature" title="networkx.utils.decorators.argmap.signature"><code class="xref py py-func docutils literal notranslate"><span class="pre">argmap.signature()</span></code></a>. This is constructed
using <a class="reference external" href="https://docs.python.org/3/library/inspect.html#inspect.signature" title="(in Python v3.11)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">inspect.signature</span></code></a> but enhanced with attribute
strings <code class="xref py py-obj docutils literal notranslate"><span class="pre">sig_def</span></code> and <code class="xref py py-obj docutils literal notranslate"><span class="pre">sig_call</span></code>, and other information
specific to mapping arguments of this function.
This information is used to construct a string of code defining
the new decorated function.</p>
</dd>
<dt>wrapped_name<span class="classifier">a unique internally used name constructed by argmap</span></dt><dd><p>for the decorated function.</p>
</dd>
<dt>functions<span class="classifier">a dict of the functions used inside the code of this</span></dt><dd><p>decorated function, to be used as <a class="reference external" href="https://docs.python.org/3/library/functions.html#globals" title="(in Python v3.11)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">globals</span></code></a> in <a class="reference external" href="https://docs.python.org/3/library/functions.html#exec" title="(in Python v3.11)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">exec</span></code></a>.
This dict is recursively updated to allow for nested decorating.</p>
</dd>
<dt>mapblock<span class="classifier">code (as a list of strings) to map the incoming argument</span></dt><dd><p>values to their mapped values.</p>
</dd>
<dt>finallys<span class="classifier">code (as a list of strings) to provide the possibly nested</span></dt><dd><p>set of finally clauses if needed.</p>
</dd>
<dt>mutable_args<span class="classifier">a bool indicating whether the <code class="xref py py-obj docutils literal notranslate"><span class="pre">sig.args</span></code> tuple should be</span></dt><dd><p>converted to a list so mutation can occur.</p>
</dd>
</dl>
</div></blockquote>
<p>After this recursive assembly process, the <a class="reference internal" href="generated/networkx.utils.decorators.argmap.compile.html#networkx.utils.decorators.argmap.compile" title="networkx.utils.decorators.argmap.compile"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap.compile</span></code></a> method
constructs code (as strings) to convert the tuple <code class="xref py py-obj docutils literal notranslate"><span class="pre">sig.args</span></code> to a list
if needed. It joins the defining code with appropriate indents and
compiles the result. Finally, this code is evaluated and the original
wrapper’s implementation is replaced with the compiled version (see
<code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap._lazy_compile</span></code> for more details).</p>
<p>Other <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> methods include <code class="xref py py-obj docutils literal notranslate"><span class="pre">_name</span></code> and <code class="xref py py-obj docutils literal notranslate"><span class="pre">_count</span></code> which allow internally
generated names to be unique within a python session.
The methods <code class="xref py py-obj docutils literal notranslate"><span class="pre">_flatten</span></code> and <code class="xref py py-obj docutils literal notranslate"><span class="pre">_indent</span></code> process the nested lists of strings
into properly indented python code ready to be compiled.</p>
<p>More complicated nested tuples of arguments also allowed though
usually not used. For the simple 2 argument case, the argmap
input (“a”, “b”) implies the mapping function will take 2 arguments
and return a 2-tuple of mapped values. A more complicated example
with argmap input <code class="xref py py-obj docutils literal notranslate"><span class="pre">("a",</span> <span class="pre">("b",</span> <span class="pre">"c"))</span></code> requires the mapping function
take 2 inputs, with the second being a 2-tuple. It then must output
the 3 mapped values in the same nested structure <code class="xref py py-obj docutils literal notranslate"><span class="pre">(newa,</span> <span class="pre">(newb,</span> <span class="pre">newc))</span></code>.
This level of generality is not often needed, but was convenient
to implement when handling the multiple arguments.</p>
<p class="rubric">Examples</p>
<p>Most of these examples use <code class="xref py py-obj docutils literal notranslate"><span class="pre">@argmap(...)</span></code> to apply the decorator to
the function defined on the next line.
In the NetworkX codebase however, <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> is used within a function to
construct a decorator. That is, the decorator defines a mapping function
and then uses <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> to build and return a decorated function.
A simple example is a decorator that specifies which currency to report money.
The decorator (named <code class="xref py py-obj docutils literal notranslate"><span class="pre">convert_to</span></code>) would be used like:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@convert_to</span><span class="p">(</span><span class="s2">"US_Dollars"</span><span class="p">,</span> <span class="s2">"income"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">show_me_the_money</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">income</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2"> : </span><span class="si">{</span><span class="n">income</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
</pre></div>
</div>
<p>And the code to create the decorator might be:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">convert_to</span><span class="p">(</span><span class="n">currency</span><span class="p">,</span> <span class="n">which_arg</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">_convert</span><span class="p">(</span><span class="n">amount</span><span class="p">):</span>
<span class="k">if</span> <span class="n">amount</span><span class="o">.</span><span class="n">currency</span> <span class="o">!=</span> <span class="n">currency</span><span class="p">:</span>
<span class="n">amount</span> <span class="o">=</span> <span class="n">amount</span><span class="o">.</span><span class="n">to_currency</span><span class="p">(</span><span class="n">currency</span><span class="p">)</span>
<span class="k">return</span> <span class="n">amount</span>
<span class="k">return</span> <span class="n">argmap</span><span class="p">(</span><span class="n">_convert</span><span class="p">,</span> <span class="n">which_arg</span><span class="p">)</span>
</pre></div>
</div>
<p>Despite this common idiom for argmap, most of the following examples
use the <code class="xref py py-obj docutils literal notranslate"><span class="pre">@argmap(...)</span></code> idiom to save space.</p>
<p>Here’s an example use of argmap to sum the elements of two of the functions
arguments. The decorated function:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="nb">sum</span><span class="p">,</span> <span class="s2">"xlist"</span><span class="p">,</span> <span class="s2">"zlist"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">xlist</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">zlist</span><span class="p">):</span>
<span class="k">return</span> <span class="n">xlist</span> <span class="o">-</span> <span class="n">y</span> <span class="o">+</span> <span class="n">zlist</span>
</pre></div>
</div>
<p>is syntactic sugar for:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">xlist</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">zlist</span><span class="p">):</span>
<span class="n">x</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">xlist</span><span class="p">)</span>
<span class="n">z</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">zlist</span><span class="p">)</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">-</span> <span class="n">y</span> <span class="o">+</span> <span class="n">z</span>
</pre></div>
</div>
<p>and is equivalent to (using argument indexes):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="nb">sum</span><span class="p">,</span> <span class="s2">"xlist"</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">xlist</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">zlist</span><span class="p">):</span>
<span class="k">return</span> <span class="n">xlist</span> <span class="o">-</span> <span class="n">y</span> <span class="o">+</span> <span class="n">zlist</span>
</pre></div>
</div>
<p>or:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="nb">sum</span><span class="p">,</span> <span class="s2">"zlist"</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">xlist</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">zlist</span><span class="p">):</span>
<span class="k">return</span> <span class="n">xlist</span> <span class="o">-</span> <span class="n">y</span> <span class="o">+</span> <span class="n">zlist</span>
</pre></div>
</div>
<p>Transforming functions can be applied to multiple arguments, such as:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">swap</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span>
<span class="k">return</span> <span class="n">y</span><span class="p">,</span> <span class="n">x</span>
<span class="c1"># the 2-tuple tells argmap that the map `swap` has 2 inputs/outputs.</span>
<span class="nd">@argmap</span><span class="p">(</span><span class="n">swap</span><span class="p">,</span> <span class="p">(</span><span class="s2">"a"</span><span class="p">,</span> <span class="s2">"b"</span><span class="p">)):</span>
<span class="k">def</span> <span class="nf">foo</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="n">c</span><span class="p">):</span>
<span class="k">return</span> <span class="n">a</span> <span class="o">/</span> <span class="n">b</span> <span class="o">*</span> <span class="n">c</span>
</pre></div>
</div>
<p>is equivalent to:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">foo</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="n">c</span><span class="p">):</span>
<span class="n">a</span><span class="p">,</span> <span class="n">b</span> <span class="o">=</span> <span class="n">swap</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="k">return</span> <span class="n">a</span> <span class="o">/</span> <span class="n">b</span> <span class="o">*</span> <span class="n">c</span>
</pre></div>
</div>
<p>More generally, the applied arguments can be nested tuples of strings or ints.
The syntax <code class="xref py py-obj docutils literal notranslate"><span class="pre">@argmap(some_func,</span> <span class="pre">("a",</span> <span class="pre">("b",</span> <span class="pre">"c")))</span></code> would expect <code class="xref py py-obj docutils literal notranslate"><span class="pre">some_func</span></code> to
accept 2 inputs with the second expected to be a 2-tuple. It should then return
2 outputs with the second a 2-tuple. The returns values would replace input “a”
“b” and “c” respectively. Similarly for <code class="xref py py-obj docutils literal notranslate"><span class="pre">@argmap(some_func,</span> <span class="pre">(0,</span> <span class="pre">("b",</span> <span class="pre">2)))</span></code>.</p>
<p>Also, note that an index larger than the number of named parameters is allowed
for variadic functions. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">double</span><span class="p">(</span><span class="n">a</span><span class="p">):</span>
<span class="k">return</span> <span class="mi">2</span> <span class="o">*</span> <span class="n">a</span>
<span class="nd">@argmap</span><span class="p">(</span><span class="n">double</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">overflow</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">):</span>
<span class="k">return</span> <span class="n">a</span><span class="p">,</span> <span class="n">args</span>
<span class="nb">print</span><span class="p">(</span><span class="n">overflow</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> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">))</span> <span class="c1"># output is 1, (2, 3, 8, 5, 6)</span>
</pre></div>
</div>
<p><strong>Try Finally</strong></p>
<p>Additionally, this <a class="reference internal" href="#networkx.utils.decorators.argmap" title="networkx.utils.decorators.argmap"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argmap</span></code></a> class can be used to create a decorator that
initiates a try…finally block. The decorator must be written to return
both the transformed argument and a closing function.
This feature was included to enable the <a class="reference internal" href="networkx.utils.decorators.open_file.html#networkx.utils.decorators.open_file" title="networkx.utils.decorators.open_file"><code class="xref py py-obj docutils literal notranslate"><span class="pre">open_file</span></code></a> decorator which might
need to close the file or not depending on whether it had to open that file.
This feature uses the keyword-only <code class="xref py py-obj docutils literal notranslate"><span class="pre">try_finally</span></code> argument to <code class="xref py py-obj docutils literal notranslate"><span class="pre">@argmap</span></code>.</p>
<p>For example this map opens a file and then makes sure it is closed:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">open_file</span><span class="p">(</span><span class="n">fn</span><span class="p">):</span>
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">fn</span><span class="p">)</span>
<span class="k">return</span> <span class="n">f</span><span class="p">,</span> <span class="k">lambda</span><span class="p">:</span> <span class="n">f</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>The decorator applies that to the function <code class="xref py py-obj docutils literal notranslate"><span class="pre">foo</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="n">open_file</span><span class="p">,</span> <span class="s2">"file"</span><span class="p">,</span> <span class="n">try_finally</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">file</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
</pre></div>
</div>
<p>is syntactic sugar for:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="n">file</span><span class="p">,</span> <span class="n">close_file</span> <span class="o">=</span> <span class="n">open_file</span><span class="p">(</span><span class="n">file</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="n">file</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">close_file</span><span class="p">()</span>
</pre></div>
</div>
<p>and is equivalent to (using indexes):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="n">open_file</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">try_finally</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">file</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
</pre></div>
</div>
<p>Here’s an example of the try_finally feature used to create a decorator:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">my_closing_decorator</span><span class="p">(</span><span class="n">which_arg</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">_opener</span><span class="p">(</span><span class="n">path</span><span class="p">):</span>
<span class="k">if</span> <span class="n">path</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="n">path</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">path</span><span class="p">)</span>
<span class="n">fclose</span> <span class="o">=</span> <span class="n">path</span><span class="o">.</span><span class="n">close</span>
<span class="k">else</span><span class="p">:</span>
<span class="c1"># assume `path` handles the closing</span>
<span class="n">fclose</span> <span class="o">=</span> <span class="k">lambda</span><span class="p">:</span> <span class="kc">None</span>
<span class="k">return</span> <span class="n">path</span><span class="p">,</span> <span class="n">fclose</span>
<span class="k">return</span> <span class="n">argmap</span><span class="p">(</span><span class="n">_opener</span><span class="p">,</span> <span class="n">which_arg</span><span class="p">,</span> <span class="n">try_finally</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
</pre></div>
</div>
<p>which can then be used as:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@my_closing_decorator</span><span class="p">(</span><span class="s2">"file"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">fancy_reader</span><span class="p">(</span><span class="n">file</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="c1"># this code doesn't need to worry about closing the file</span>
<span class="nb">print</span><span class="p">(</span><span class="n">file</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
</pre></div>
</div>
<p>Decorators with try_finally = True cannot be used with generator functions,
because the <code class="xref py py-obj docutils literal notranslate"><span class="pre">finally</span></code> block is evaluated before the generator is exhausted:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@argmap</span><span class="p">(</span><span class="n">open_file</span><span class="p">,</span> <span class="s2">"file"</span><span class="p">,</span> <span class="n">try_finally</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">file_to_lines</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">file</span><span class="o">.</span><span class="n">readlines</span><span class="p">():</span>
<span class="k">yield</span> <span class="n">line</span>
</pre></div>
</div>
<p>is equivalent to:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">file_to_lines_wrapped</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">file</span><span class="o">.</span><span class="n">readlines</span><span class="p">():</span>
<span class="k">yield</span> <span class="n">line</span>
<span class="k">def</span> <span class="nf">file_to_lines_wrapper</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">file</span> <span class="o">=</span> <span class="n">open_file</span><span class="p">(</span><span class="n">file</span><span class="p">)</span>
<span class="k">return</span> <span class="n">file_to_lines_wrapped</span><span class="p">(</span><span class="n">file</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">file</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>which behaves similarly to:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">file_to_lines_whoops</span><span class="p">(</span><span class="n">file</span><span class="p">):</span>
<span class="n">file</span> <span class="o">=</span> <span class="n">open_file</span><span class="p">(</span><span class="n">file</span><span class="p">)</span>
<span class="n">file</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">file</span><span class="o">.</span><span class="n">readlines</span><span class="p">():</span>
<span class="k">yield</span> <span class="n">line</span>
</pre></div>
</div>
<p>because the <code class="xref py py-obj docutils literal notranslate"><span class="pre">finally</span></code> block of <code class="xref py py-obj docutils literal notranslate"><span class="pre">file_to_lines_wrapper</span></code> is executed before
the caller has a chance to exhaust the iterator.</p>
<dl class="py method">
<dt class="sig sig-object py" id="networkx.utils.decorators.argmap.__init__">
<span class="sig-name descname"><span class="pre">__init__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">func</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">try_finally</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="../../_modules/networkx/utils/decorators.html#argmap.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#networkx.utils.decorators.argmap.__init__" title="Permalink to this definition">#</a></dt>
<dd></dd></dl>
<p class="rubric">Methods</p>
<table class="autosummary longtable table autosummary">
<tbody>
<tr class="row-odd"><td><p><a class="reference internal" href="generated/networkx.utils.decorators.argmap.assemble.html#networkx.utils.decorators.argmap.assemble" title="networkx.utils.decorators.argmap.assemble"><code class="xref py py-obj docutils literal notranslate"><span class="pre">assemble</span></code></a>(f)</p></td>
<td><p>Collects components of the source for the decorated function wrapping f.</p></td>
</tr>
<tr class="row-even"><td><p><a class="reference internal" href="generated/networkx.utils.decorators.argmap.compile.html#networkx.utils.decorators.argmap.compile" title="networkx.utils.decorators.argmap.compile"><code class="xref py py-obj docutils literal notranslate"><span class="pre">compile</span></code></a>(f)</p></td>
<td><p>Compile the decorated function.</p></td>
</tr>
<tr class="row-odd"><td><p><a class="reference internal" href="generated/networkx.utils.decorators.argmap.signature.html#networkx.utils.decorators.argmap.signature" title="networkx.utils.decorators.argmap.signature"><code class="xref py py-obj docutils literal notranslate"><span class="pre">signature</span></code></a>(f)</p></td>
<td><p>Construct a Signature object describing <code class="xref py py-obj docutils literal notranslate"><span class="pre">f</span></code></p></td>
</tr>
</tbody>
</table>
</dd></dl>
</section>
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