<p>您必须确保,任何应该返回某些内容的函数都会以各种方式执行此操作,以结束函数。你知道吗</p>
<p>函数<code>file_in_english</code>只返回<code>if characters > character_limit:</code>情况下的某些内容</p>
<p>如果<code>charachter ==</code>或<code>charachter < character_limit</code>不是</strong>这种情况,则函数不显式返回任何内容。你知道吗</p>
<p><em>任何</em>函数如果不从它返回某些内容,则在它返回到调用方时隐式返回<code>None</code>。你知道吗</p>
<pre><code>def something(boolean):
"""Function that only returns something meaninfull if boolean is True."""
if boolean:
return "Wow"
print(something(True)) # returns Wow
print(something(False)) # implicitly returns/prints None
</code></pre>
<p>您可以在python教程中找到这一事实:</p>
<blockquote>
<p>Coming from other languages, you might object that fib is not a
function but a procedure since it doesn’t return a value. In fact,
even functions without a return statement do return a value, albeit a
rather boring one. This value is called None (it’s a built-in name).
Writing the value None is normally suppressed by the interpreter if it
would be the only value written. You can see it if you really want to
using print():</p>
</blockquote>
<p>来源:<a href="https://docs.python.org/3.7/tutorial/controlflow.html#defining-functions" rel="nofollow noreferrer">https://docs.python.org/3.7/tutorial/controlflow.html#defining-functions</a>-就在第二个绿色示例框之后</p>