Mixing
How to call a function within a class with self
How to call a function within a class with self
Suppose I have the following:
class myClass:
def foo(self):
# do something
How can I call myClass from inside the class without declaring an new myClass Object? i.e. I'd like something like
myClass
myClass
class myClass:
def foo(self):
# do something
if __name__ == '__main__':
# call foo
or without main:
main
class myClass:
def foo(self):
# do something
# call foo
Right now I keep getting either the error that self is not defined, or the error that foo expects 1 argument but 0 was provided.
self
foo
1
0
foo
myClass
you can use
foo as a classmethod to achieve this.– Soumendra
Jun 29 at 17:23
foo
classmethod
@Soumendra If the OP really wants to call the function from inside the class statement, there's no class yet either. (Strictly speaking,
foo can be called immediately as a regular function, although providing the correct arguments may be problematic.)– chepner
Jun 29 at 17:58
foo
@chepner, yeah, correct. I missed the indentation and thought OP try to call from outside of the class. Thanks.
– Soumendra
Jun 29 at 18:07
2 Answers
2
You cannot. The function is part of the class, so to access it you must access the class first.
class myClass:
def foo(self):
# do something
myClass().foo()
If you just don't want to type myClass().foo() but only foo then you could just return the myClass() in a new function called foo():
myClass().foo()
foo
myClass()
foo()
def foo():
return myClass().foo()
You can use self in a class when calling from inside the class itself:
self
class myClass:
def __init__(self):
pass
def foo(self):
pass
def method2(self):
self.foo()
This does not create a new instance of myClass like calling myClass().foo() would, and you do not need to pass the same arguments that you may have passed in myClass.
myClass
myClass().foo()
myClass
Since foo() has a self parameter, that means it is an instance method, and therefore it is only callable from an instance of myClass.
foo()
self
myClass
If you want foo to be callable without an instance, use the @staticmethod decorator, and remove self from the parameter list.
foo
@staticmethod
self
Technically, it's an instance method because it's a function defined in the body of a
class statement and it isn't decorated by either @classmethod or @staticmethod; the self parameter just means the function is prepared to receive the argument it will be passed when called.– chepner
Jun 29 at 17:28
class
@classmethod
@staticmethod
self
@chepner You're right of course,
self is not a magical name. But in an effort to preserve my sanity, I'm deliberately ignoring any use of self outside of its widely accepted meaning.– John Gordon
Jun 29 at 17:42
self
self
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You can't, because that doesn't make any sense. If you want
footo be callable without amyClassinstance, why is it an instance method?– Aran-Fey
Jun 29 at 17:19