[Python3] I made a decorator that declares undefined functions and methods.

1. Preparation

Create the following module (= py file) and do import.


class undefined error(Exception):
    def __init__(self, f): super().__init__(str(f)+"Is undefined.")
class undefined:
    def __init__(self, f):raise undefined error(f)
class undefined method:
    def __init__(self, m): self.m = m
    def __call__(self, *_, **__): raise Error(self.m)

2. How to use

2-1. In-function function (if not an object-oriented method)

First, put the decorator @ undefined on top of the undefined function def as follows.


from undefined import*

def f_out():
    def f_in():pass
    return f_in

And when we evaluate f_out (), we get:

Undefined Error: f_in is undefined

Traceback (most recent call last):
  File "<pyshell#301>", line 1, in <module>
  File "~~~~.py", line 104, in f_out
    def f_in():pass
  File "~~~~.py", line 100, in __init__
raise undefined error(f)
Undefined Error: <function f_out.<locals>.f_in at 0x0000023470EFADC0>Is undefined

2-2. For object-oriented methods

First, add the decorator @ undefined method on top of the undefined method def as follows.


class Test:
    def __init__(self):pass

    @Undefined method
    def mtd(self):pass

And when we evaluate Test (). Mtd (), we get:

Undefined Error: Test.mtd is undefined

Traceback (most recent call last):
  File "<pyshell#309>", line 1, in <module>
  File "~~~~.py", line 101, in __call__
    def __call__(self, *args, **kwargs):raise undefined error(self.m)
Undefined Error: <function Test.mtd at 0x0000021AD5D3AF70>Is undefined

Note: When you create a method in a class, the processing system executes the method once without explicitly calling the class or its object. Method (*). Therefore, if you simply replace @ undefined method with @ undefined, when an undefined method exists, even if the class is never called or an object is not created, it is undefined. It will now return Error.

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