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

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, Sep 13 '19 at 19:44

score 2 · Accepted Answer · answered Sep 13 '19 at 19:44

2

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 '19 at 19:44

SergeyA

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Thank you! Does that mean it's preferable to write "if simple_condition() and complex_condition():" than the other way around? – Joseph Sep 13 '19 at 19:53
@Joseph I think so. – SergeyA Sep 13 '19 at 19:56

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

1 Answers1