Why does pycharm propose to change method to stati

问题:

The new pycharm release (3.1.3 community edition) proposes to convert the methods that don't work with the current object's state to static.

What is the practical reason for that? Some kind of micro-performance(-or-memory)-optimization?

回答1:

PyCharm "thinks" that you might have wanted to have a static method, but you forgot to declare it to be static.

PyCharm proposes this because the method does not use self in its body and hence does not actually change the class instance. Hence the method could be static, i.e. callable without having created a class instance before.

回答2:

Agreed with @jolvi, @ArundasR, and others, the warning happens on a member function that doesn't use self.

If you're sure PyCharm is wrong, that the function should not be a @staticmethod, and if you value zero warnings, you can make this one go away two different ways:

Workaround #1

def bar(self):
    self.is_not_used()
    doing_something_without_self()

def is_not_used(self):
    pass

Workaround #2 ^{[Thanks @DavidPärsson]}

# noinspection PyMethodMayBeStatic
def bar(self):
    doing_something_without_self()

The application I had for this (the reason I could not use @staticmethod) was in making a table of handler functions for responding to a protocol subtype field. All handlers had to be the same form of course (static or nonstatic). But some didn't happen to do anything with the instance. If I made those static I'd get "TypeError: 'staticmethod' object is not callable".

In support of the OP's consternation, suggesting you add staticmethod whenever you can, goes against the principle that it's easier to make code less restrictive later, than to make it more -- making a method static makes it less restrictive now, in that you can call class.f() instead of instance.f().

Guesses as to why this warning exists:

• It advertises staticmethod. It makes developers aware of something they may well have intended.
• As @JohnWorrall's points out, it gets your attention when self was inadvertently left out of the function.
• It's a cue to rethink the object model; maybe the function does not belong in this class at all.

回答3:

I think that the reason for this warning is config in Pycharm. You can uncheck the selection Method may be static in Editor->Inspection

回答4:

I can imagine following advantages of having a class method defined as static one:

• you can call the method just using class name, no need to instantiate it.

remaining advantages are probably marginal if present at all:

• might run a bit faster
• save a bit of memory

回答5:

I agree with the answers given here (method does not use self and therefore could be decorated with @staticmethod).

I'd like to add that you maybe want to move the method to a top-level function instead of a static method inside a class. For details see this question and the accepted answer: python - should I use static methods or top-level functions

Moving the method to a top-level function will fix the PyCharm warning, too.

回答6:

This error message just helped me a bunch, as I hadn't realized that I'd accidentally written my function using my testing example player

my_player.attributes[item] 

instead of the correct way

self.attributes[item]

回答7:

Since you didn't refer to self in the bar method body, PyCharm is asking if you might have wanted to make bar static. In other programming languages, like Java, there are obvious reasons for declaring a static method. In Python, the only real benefit to a static method (AFIK) is being able to call it without an instance of the class. However, if that's your only reason, you're probably better off going with a top-level function - as note here.

In short, I'm not one hundred percent sure why it's there. I'm guessing they'll probably remove it in an upcoming release.