擅长:python、mysql、java
<p>这:</p>
<pre><code>def do_nothing(*args):
pass
</code></pre>
<p>相当于:</p>
<pre><code>lambda *args: None
</code></pre>
<p>一个是<code>lambda</code>,一个不是(例如,<code>__name__</code>在函数上是<code>do_nothing</code>,在lambda上是<code><lambda></code>)。如果这对你很重要,不要忘记<code>**kwargs</code>。Python中没有显式<code>return <x></code>返回<code>None</code>的函数。这是<a href="http://docs.python.org/2/reference/expressions.html#calls">here</a>:</p>
<blockquote>
<p>A call always returns some value, possibly None, unless it raises an exception.</p>
</blockquote>
<p>我使用了类似的函数作为默认值,例如:</p>
<pre><code>def long_running_code(progress_function=lambda percent_complete: None):
# Report progress via progress_function.
</code></pre>