Is it Pythonic to use list comprehensions for just side effects?

python list-comprehension
sinan picture sinan · Apr 22, 2011 · Viewed 10.4k times · Source

Think about a function that I'm calling for its side effects, not return values (like printing to screen, updating GUI, printing to a file, etc.).

def fun_with_side_effects(x):
    ...side effects...
    return y

Now, is it Pythonic to use list comprehensions to call this func:

[fun_with_side_effects(x) for x in y if (...conditions...)]

Note that I don't save the list anywhere

Or should I call this func like this:

for x in y:
    if (...conditions...):
        fun_with_side_effects(x)

Which is better and why?

Answer

Ignacio Vazquez-Abrams picture Ignacio Vazquez-Abrams · Apr 22, 2011

It is very anti-Pythonic to do so, and any seasoned Pythonista will give you hell over it. The intermediate list is thrown away after it is created, and it could potentially be very, very large, and therefore expensive to create.

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