CODEWITHSUNDEEP
pythonpython-3.xmypy
addsub1234
addsub1234

Reputation: 53

How to create statically typed python class with same typed member

I am from java background, learning python. I am trying to create a python class (with static typing), containing a member of same class.

mynode.py 

class MyNode():
    def __init__(self, id: str=None, child_node: MyNode=None):
        self._id = id
        self._child_node = child_node

main.py 

import mynode

def main():
    n1 = MyNode('child1')

if __name__ == '__main__':
    main()

But the following errors are occurring while executing. How can this be resolved ?

...\py-tests>python main.py
Traceback (most recent call last):
  File "main.py", line 1, in <module>
    import mynode
  File "...\py-tests\mynode.py", line 1, in <module>
    class MyNode():
  File "...\py-tests\mynode.py", line 2, in MyNode
    def __init__(self, id: str=None, child_node: MyNode=None):
NameError: name 'MyNode' is not defined

Upvotes: 2

Views: 56

Answers (1)

chepner
chepner

Reputation: 531165

At the time __init__ is being defined, the class itself isn't yet defined, let alone bound to a name. Use a forward reference instead, consisting of a string literal.

class MyNode:
    def __init__(self, id: str = None, child_node: 'MyNode' = None):

Upvotes: 2

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