global() function for list in python

Question

Python: 3.8.1

I am unable to append data in class variables using global() function.

class test():
    __cv__ = []

        def testglobalmethod(self, data):
            globals()['__cv__']=[data]
            print(__cv__)


    rrr = test()
    rrr.testglobalmethod("1")
    rrr.testglobalmethod("2")

Expected Results:- ['1','2']

Actual Results:- ['1'] ['2']

The append function produces below error:-

def testglobalmethod(self, data):
    globals()['__cv__'].append(data)
    print(__cv__)

Error: KeyError: '__cv__'

@wim I have learned the global() function recently. I tried with string and worked perfectly fine. So, I am trying with the list to see how it works. — Learner
– Learner, Commented Feb 19, 2020 at 16:56
__cv__ isn't global, it's a class attribute. Why do you expect to be able to access it via globals? Is it intentional that all your code is part of the test class scope? — MisterMiyagi
– MisterMiyagi, Commented Feb 19, 2020 at 16:57
Don't invent your own dunder names; they are reserved for use by the language itself. Just use cv, or _cv if you want to emphasize that it is for use by methods of the test class alone. — chepner
– chepner, Commented Feb 19, 2020 at 16:57

Daniel · Accepted Answer · 2020-02-19 16:55:12Z

2

You have a class attribute, not a global variable.

class Test():
    __cv__ = []

    def testglobalmethod(self, data):
        Test.__cv__.append(data)
        print(Test.__cv__)


rrr = Test()
rrr.testglobalmethod("1")
rrr.testglobalmethod("2")

answered Feb 19, 2020 at 16:55

Daniel

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