Does Python Check ALL conditions in an multi-condition if statement? [duplicate]

Question

I am curious if Python will continue checking conditions in an if statement if the first condition returns False. I'm wondering about this because I want to know if best practice is try to check conditions with low time-complexity before more complex checks.

Is there any difference between these two snippets?

if condition_1() and condition_2():
    do_something()

and

if condition_1():
    if condition_2():
        do_something()

There is no difference. Python will lazily evaluate the boolean conditions left to right in an if statement. If condition_1() is False, it will not try to evaluate condition_2(). — James
– James, Commented Sep 13, 2019 at 19:44

SergeyA · Accepted Answer · 2019-09-13 19:44:12Z

3

Yes, python boolean operators do short-circuit

Both code samples are semantically equivalent, but the first is more readable, as it has lower level of nesting.

answered Sep 13, 2019 at 19:44

SergeyA

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2 Comments

Joseph Over a year ago

Thank you! Does that mean it's preferable to write "if simple_condition() and complex_condition():" than the other way around?

SergeyA Over a year ago

@Joseph I think so.

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