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    <p>Are you talking about <a href="https://docs.python.org/3.5/tutorial/controlflow.html#lambda-expressions" rel="noreferrer">lambda functions</a>? Like</p> <pre><code>lambda x: x**2 + 2*x - 5 </code></pre> <p>Those things are actually quite useful. Python supports a style of programming called <em>functional programming</em> where you can pass functions to other functions to do stuff. Example:</p> <pre><code>mult3 = filter(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, 6, 7, 8, 9]) </code></pre> <p>sets <code>mult3</code> to <code>[3, 6, 9]</code>, those elements of the original list that are multiples of 3. This is shorter (and, one could argue, clearer) than</p> <pre><code>def filterfunc(x): return x % 3 == 0 mult3 = filter(filterfunc, [1, 2, 3, 4, 5, 6, 7, 8, 9]) </code></pre> <p>Of course, in this particular case, you could do the same thing as a list comprehension:</p> <pre><code>mult3 = [x for x in [1, 2, 3, 4, 5, 6, 7, 8, 9] if x % 3 == 0] </code></pre> <p>(or even as <code>range(3,10,3)</code>), but there are many other, more sophisticated use cases where you can't use a list comprehension and a lambda function may be the shortest way to write something out.</p> <ul> <li><p>Returning a function from another function</p> <pre><code>&gt;&gt;&gt; def transform(n): ... return lambda x: x + n ... &gt;&gt;&gt; f = transform(3) &gt;&gt;&gt; f(4) 7 </code></pre> <p>This is often used to create function wrappers, such as Python's decorators.</p></li> <li><p>Combining elements of an iterable sequence with <code>reduce()</code></p> <pre><code>&gt;&gt;&gt; reduce(lambda a, b: '{}, {}'.format(a, b), [1, 2, 3, 4, 5, 6, 7, 8, 9]) '1, 2, 3, 4, 5, 6, 7, 8, 9' </code></pre></li> <li><p>Sorting by an alternate key</p> <pre><code>&gt;&gt;&gt; sorted([1, 2, 3, 4, 5, 6, 7, 8, 9], key=lambda x: abs(5-x)) [5, 4, 6, 3, 7, 2, 8, 1, 9] </code></pre></li> </ul> <p>I use lambda functions on a regular basis. It took me a while to get used to them, but eventually I came to understand that they're a very valuable part of the language.</p>
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