Sergey Kishchenko a écrit :
In Python empty container equals False in 'if' statements:
Yes.
# prints "It's ok"
if not []:
print "It's ok"
Let's create a simple Foo class:
class Foo:
pass
Now I can use Foo objects in 'if' statements:
Yes.
#prints "Ouch!"
f=Foo()
if f:
print "Ouch!"
So, default __nonzero__ impl is to return True.
Yes. It's clearly documented FWIW.
I think, this
behaviour conflicts with 'Explicit is better than implicit'
Why so ? It *is* explicit that the default for an object is to have a
true value in a boolean context.
and
'Practicality beats purity'
Quite on the contrary. From a practical POV, the default truth values of
Python objects are most of the time what you practically want in a
boolean context - that is, any non-None object, non-empty sequence and
non-zero numeric objects are true. __nonzero__ is here for the *very
few* corner cases where this is not the sensible default.
statements. I think, throwing a TypeError
exception would be better. It will result in more explicit code with
fewer errors.
I can understand that you've been bitten by the rules regarding truth
values of Python objects. But if so, please remember that it's only
because *you* assumed something different from what's documented.
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