0 == False but [] != False? - comp.lang.python

Message from discussion 0 == False but [] != False?

Rex Turnbull

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More options May 24 2007, 9:21 pm

Newsgroups: comp.lang.python

From: Rex Turnbull <rex@no_spam.dicad.de>

Date: Thu, 24 May 2007 13:21:50 +0200

Local: Thurs, May 24 2007 9:21 pm

Subject: Re: 0 == False but [] != False?

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Steven D'Aprano :

> On Thu, 24 May 2007 06:59:32 +0000, Tim Roberts wrote:

>> As a general rule, I've found code like "if x == False" to be a bad idea in
>> ANY language.

> Surely that should be written as "if (x == False) == True"?

Why compare to False?

" if not x : ... "

It really doesn't matter if x is False or if it evaluates to False. Many
things evaluate to False like [], (), 0, "", None and a few other things.

>>> def tf(thing):
... if thing : print "True thing", thing
... elif not thing : print "False thing",thing
... else : print "No thing"
...
>>> tf([])
False thing []
>>> tf([1])
True thing [1]
>>> a = ()
>>> tf(a)
False thing ()
>>> a=(0)
>>> tf(a)
False thing 0
>>> a= (1,2,3)
>>> tf(a)
True thing (1, 2, 3)
>>> tf("abc")
True thing abc
>>> tf("")
False thing
>>>

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