Python - overwrite variable from another class?

Question

Simple question that i cant figure out: I have (example) file one with this:

class foo:
var = 1
def bar(self):
    print(self.var)

if __name__ == "__main__":
    foo().bar()

and file2 with this:

from testing import foo

class foo2:
    def bar2(self):
        foo().var = 2
        foo().bar()


foo2().bar2()

It returns 1, so no overwriting happening here.

I cant figure out how to actually overwrite the variable of the imported class instance. I checked this and this but that didnt help me. Sorry for asking such a simple question, thanks in advance.

foo is a class, foo() is an instance. You seems to mix those notions. — Guillaume
– Guillaume, Commented Oct 4, 2018 at 14:32
Possible duplicate of python: class attributes and instance attributes — Guillaume
– Guillaume, Commented Oct 4, 2018 at 14:34
But i created an instance in file2 didnt i? What would the working code have changed? — Flying Thunder
– Flying Thunder, Commented Oct 4, 2018 at 14:38

Matt Messersmith · Accepted Answer · 2018-10-04 14:44:15Z

1

It is being overwritten, but you're discarding the object immediately. foo().var = 2 creates an anonymous foo object, and assigns it's var to 2. The problem is you're not keeping a reference to the foo object you've just created. Then, foo().bar() creates a new foo object, which has var == 1 (just like all new foo objects since that's what your class does) and also calls the bar() member function on this new foo object, which will print 1 to console.

Try this instead:

def bar2(self):
    foo_obj = foo()
    foo_obj.var = 2
    foo_obj.bar()

edited Oct 4, 2018 at 14:44

answered Oct 4, 2018 at 14:39

Matt Messersmith

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1 Comment

Flying Thunder Over a year ago

Damn, i just came back to python and the difference between foo, foo() and f1=foo() always confused me. Thanks! Additional question: Are there cases where what i did ("annymous" asignment) are ever useful?

NickNick · Accepted Answer · 2018-10-04 14:53:40Z

0

When you're doing foo().bar() , you're creating a second instance.

Try this:

    test = foo()
    test.var = 2
    test.bar()
 #   foo().var = 2
 #   foo().bar()

answered Oct 4, 2018 at 14:53

NickNick

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