Check if a function returns false in Python

Question

In python, I am currently doing this:

if user_can_read(request.user, b) == False:

Is there any other way of checking if the function returns False?

The BDFL suggests explicitly checking if the return value is an instance of bool and nhahtdh's method if you specifically want to compare with False and not just any falsy value, since is False is nearly always a bug. — Wooble
– Wooble, Commented Aug 23, 2012 at 18:42

John · Accepted Answer · 2012-08-23 18:33:13Z

48

You could just use

if user_can_read(request.user, b):
    ## do stuff

If user_can_read returns anything (except 0, False, etc), it will be considered True, and do stuff.

And the negation: if not user_can_read(request.user, b)

answered Aug 23, 2012 at 18:33

John

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3 Comments

Joel Cornett Over a year ago

@iyrag: As a side note, a common mistake is to assume that negative numbers evaluate to False. This is wrong, bool(-1) evaluates to True.

Adam Rosenfield Over a year ago

@Joel: People really believe that negative numbers evaluate to False? That surprises me.

Joel Cornett Over a year ago

@AdamRosenfield: I've come across this a few times. It probably stems from the fact that traditionally, a search with no result should return -1 (since 0 is taken up by the first index).

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