Default values of arguments with the same id

[DrVictor]

Ah, the good old mutable defaults...

https://python-forum.io/Thread-Basic-Var...on-Gotchas has an explanation of what's going on.
Search for "empty list".

Thank you for your answer.
According to you, I searched the internet.
And I used the following solution

class test:
    def __init__(self,val=None):
        if val==None:val=[]
        self.val=val

Writing the third line sounds a little silly but I have to.This reduces the readability of Python.
I think for other people with a different id is more useful than the same id.