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I want to edit python builtin classes and make something like Extension methods in Dart language.

extension NumberParsing on String {
  int parseInt() {
    return int.parse(this);
  }
}

any work around because python ignores any changes in the builtins.py file and I do not want to use subclasses

Mohammad Aboul-Ela
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  • Maybe you can try MonkeyPatching? https://stackoverflow.com/questions/5626193/what-is-monkey-patching – Gonzalo Odiard Oct 26 '22 at 03:29
  • You could use composition instead of inheritance in order to avoid subclassing, but this could require a lot of wrapper methods if you want to still use many of the composing class's methods. – Michael Ruth Oct 26 '22 at 19:03

1 Answers1

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You actually can overwrite builtins, but there is almost always a better way to do it. Typically subclassing the builtin is that better path. That being said, without knowing your use case I can't say for certain that it would be bad to overwrite the builtin, so here ya go.

Try this runnable example 

#!/usr/bin/env python
import builtins

class WackyStr(str):
    def __new__(cls, s):
        if s.isnumeric():
            return int(s)
        if s.replace('.','').isnumeric():
            return float(s)
        return super().__new__(cls, s)

builtins.str = WackyStr

if __name__ == "__main__":
    a = str("two")
    b = str("2.0")
    c = str("2")
    print(f"{a=}, {type(a)=}")
    print(f"{b=}, {type(b)=}")
    print(f"{c=}, {type(c)=}")
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My recommendation though would be to not overwrite the builtin and just use your new class 

#!/usr/bin/env python
class WackyStr(str):
    def __new__(cls, s):
        if s.isnumeric():
            return int(s)
        if s.replace('.','').isnumeric():
            return float(s)
        return super().__new__(cls, s)

if __name__ == "__main__":
    a = WackyStr("two")
    b = WackyStr("2.0")
    c = WackyStr("2")
    print(f"{a=}, {type(a)=}")
    print(f"{b=}, {type(b)=}")
    print(f"{c=}, {type(c)=}")
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Modularizer
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