python instance function do not find type(class)

Question

TestX is class has mylist as property, mylist returns the collection of TestX objects, below is the sample code, at line #5 getting an error "'TestX' is not declared", if TestX is removed then no error code works fine, the only question here why Python do not recognize type name in same type at collection, if preemptive/system types like int, str etc.. then type name is recognized.

class TestX:
    def __init__(self) -> None:
        self._mylist:list[TestX] = [] 

    def _get_mylist(self)->list[TestX]: #This line error out
        return self._mylist

    def _set_mylist(self,value):
        self._mylist = value

    mylist = property(fget=_get_mylist,fset=_set_mylist,doc="This is test")

def main():
    test = TestX()
    print(len(test.mylist))
    test.mylist = [TestX()]
    print(len(test.mylist))

if __name__ == "__main__":
    main()

Result

Traceback (most recent call last):   
    File "D:\code\test.py", line 1, in <module>
        class TestX:   
    File "D:\code\test.py", line 5, in TestX
        def _get_mylist(self)->list[TestX]: 
NameError: name 'TestX' is not defined

You should use the solution in the linked duplicate above – juanpa.arrivillaga Sep 19 '22 at 18:16 — juanpa.arrivillaga, Sep 19 '22 at 18:16

bitflip · Accepted Answer · 2022-09-19T18:27:17.330

0

You can use

def _get_mylist(self) -> list['TestX']:

edited Sep 19 '22 at 18:27

answered Sep 19 '22 at 17:16

bitflip

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This is *absolutely incorrect* – juanpa.arrivillaga Sep 19 '22 at 18:15
@Hi10 do not type annotate with `__class__` – juanpa.arrivillaga Sep 19 '22 at 18:15
Someone commented to better use `__class__` instead of a string, so i added it. I removed it again to examine your objection. Using a str seems to be the preferred way. – bitflip Sep 19 '22 at 18:39
Yes, I did test and hence edited comment to review. – Hi10 Sep 19 '22 at 19:26
@bitflip `__class__` is completely wrong. Using a string is fine, you can also use `from __future__ import annotations` and this won't raise an error anymore with `list[TestX]`, this is all explained in the linked duplicate – juanpa.arrivillaga Sep 19 '22 at 20:51

python instance function do not find type(class)

1 Answers1