问题
Which is better? (and why?)
if somevalue == False:
or
if somevalue is False:
Does your answer change if somevalue is a string?
回答1:
It rather depends on what somevalue can be: if somevalue could be anything you could check that it's a boolean and not:
if isinstance(somevalue, bool) and not somevalue
this doesn't rely on False being a singleton. If it always is a singleton you can also do:
if somevalue is False
But PEP8 of Python states you shouldn't care if it about the class and just use:
if not somevalue
this will evaluate if somevalue is "falsy". See Python documentation on Truth value testing.
PEP8 states:
Don't compare boolean values to True or False using == .
and gives these examples:
Yes: if greeting:
No: if greeting == True:
Worse: if greeting is True:
which translates in your case to:
Yes: if not greeting:
No: if greeting == False:
Worse: if greeting is False:
Keep in mind that each string is considered "truthy" except the empty string ''.
回答2:
is is checking whether two objects are literally the same object. == is checking for equality.
If you want to check whether something is false, e.g. zero, opposite of True, do if something == False.
As mentioned in the comments, you can certainly do if not something, it may improve readability quite a bit, but it's the same as if bool(something) == False.
I prefer equality, because, to my mind, True and False should behave just like 1 and 0 in terms of being true or false. For example ("a" == "a") == False evaluates to False just like ("a" == "a") == 0 does.
来源：https://stackoverflow.com/questions/37103705/what-is-the-correct-way-to-check-for-false