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  1. PO
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    <p>If you can call func() beforehand, and you want to combine the test and assignment statements into a single statement, then you can do this, with an if-else expression:</p> <pre><code>b += [a] if a is not None else [] </code></pre> <p>If a is not None, then this will add [a] to b -- essentially the same operation as b.append(a)</p> <p>If a <em>is</em> None, then this will add [] to b, which will leave b unchanged.</p> <p>This won't work unless b is a list, or at least supports "+=" in-place addition. If it doesn't -- perhaps it's some custom object, then you should be able to do this:</p> <pre><code>(b.append(a) if a is not None else None) </code></pre> <p>This is an expression, evaluated for its side effects, and then thrown away. If a is None, then the <code>b.append(a)</code> call will never be executed. In either case, the value of the expression is None, but we don't care about it, so it gets ignored.</p> <p>Now, if you want to combine the func() call with this, then you'll have to do something different in order to avoid calling func twice. If you can use the "+=" syntax, then you can do it like this:</p> <pre><code>b += filter(None, [func()]) </code></pre> <p><code>filter(None, &lt;list&gt;)</code> returns the list with all false elements (None included, but also 0 and []) removed. This statement, then, will add either [func()] or [] to b.</p> <p><strong>[Edited]</strong></p> <p>Finally, for the worst case scenario: If you can't call func() more than once, <em>and</em> you can't use <code>b += &lt;list&gt;</code>, <em>and</em> you need to accept 0, "", [], etc, and only exclude <code>None</code>, <em>and</em> you need it all on one line, here's the ugliest line of code yet:</p> <pre><code>(lambda l, a: l.append(a) if a is not None else None)(b, func()) </code></pre> <p>This is essentially @ekhumoro's solution, compressed into one line. It defines an anonymous function, calls it, discards the value, and then discards the function, all for the sake of the side effect.</p> <p>Now, this is a single line, but it's certainly not easier to read or understand than the original code. If I were you, I'd stick with the original, or go with @ekhumoro's idea of just defining a helper function and using that.</p>
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    1. POPython: avoiding if condition for this code?
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    1. USIan Clelland
    1. USIan Clelland
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    1. COProblem is, where do you call `func()`? You probably don't want to call the thing several times. I'd be really interested in seeing this solution where `a` is replaced with a function call that only gets called once (in one line).
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      1. USDonald Miner
    2. COb is actually a class of xml.etree.ElementTree so, I am not sure the [] notation can work.
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      1. USJerry Gao
    3. COwhy not just b+=[a] if a else []...instead of the if part, you would still have to call a=func() beforehand. Sorry I guess that's the part you don't like
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      1. USMatt
 

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