pandas-docstrings: Specify when random data in examples might be OK (#77)

Author: dukebody

pandas/guide/_sources/pandas_docstring.rst.txt

@@ -259,7 +259,7 @@ After the title, each parameter in the signature must be documented, including
 The parameters are defined by their name, followed by a space, a colon, another
 space, and the type (or types). Note that the space between the name and the
 colon is important. Types are not defined for `*args` and `**kwargs`, but must
-be defined for all other parameters. After the parameter definition, it is 
+be defined for all other parameters. After the parameter definition, it is
 required to have a line with the parameter description, which is indented, and
 can have multiple lines. The description must start with a capital letter, and
 finish with a dot.
@@ -840,7 +840,15 @@ be tricky. Here are some attention points:
   imported as ``import pandas as pd`` and ``import numpy as np``) and define
   all variables you use in the example.
 
-* Try to avoid using random data.
+* Try to avoid using random data. However random data might be OK in some
+  cases, like if the function you are documenting deals with probability
+  distributions, or if the amount of data needed to make the function result
+  meaningful is too much, such that creating it manually is very cumbersome.
+  In those cases, always use a fixed random seed to make the generated examples
+  predictable. Example::
+
+    >>> np.random.seed(42)
+    >>> df = pd.DataFrame({'normal': np.random.normal(100, 5, 20)})
 
 * If you have a code snippet that wraps multiple lines, you need to use '...'
   on the continued lines: ::

pandas/guide/pandas_docstring.html

@@ -764,7 +764,16 @@ <h2>About docstrings and standards<a class="headerlink" href="#about-docstrings-
 imported as <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">pandas</span> <span class="pre">as</span> <span class="pre">pd</span></code> and <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">numpy</span> <span class="pre">as</span> <span class="pre">np</span></code>) and define
 all variables you use in the example.</p>
 </li>
-<li><p class="first">Try to avoid using random data.</p>
+<li><p class="first">Try to avoid using random data. However random data might be OK in some
+cases, like if the function you are documenting deals with probability
+distributions, or if the amount of data needed to make the function result
+meaningful is too much, such that creating it manually is very cumbersome.
+In those cases, always use a fixed random seed to make the generated examples
+predictable. Example:</p>
+<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">seed</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
+<span class="gp">&gt;&gt;&gt; </span><span class="n">df</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">DataFrame</span><span class="p">({</span><span class="s1">&#39;normal&#39;</span><span class="p">:</span> <span class="n">np</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">20</span><span class="p">)})</span>
+</pre></div>
+</div>
 </li>
 <li><p class="first">If you have a code snippet that wraps multiple lines, you need to use ‘…’
 on the continued lines:</p>