[New-bugs-announce] [issue35174] Calling for super().__str__ seems to call self.__repr__ in list subclass

[Camion]

New submission from Camion <camion_spam-pybugs at yahoo.com>:

I don't know if this is by design (for what reason ?) or if it is a bug, but I have noticed this quite counter-intuitive behaviour :

Doing that, it seems that the logical way to make the __repr__ and __str__ methods, would be to override respectively the parent __repr__ and _str__ methods, and calling them from the inherited versions, but for some reason, it seems that calling super().__str__ leads to call self.__repr__.

I have written the following piece of python-3 code in which I subclass the list class in order to make a class which supports storing names and unnamed fields the same way you can have variable named and unnamed parameters in a function call :

    class struct(list):
        def __init__(self, *args, **kwargs):
            super().__init__(args)
            for key, value in kwargs.items():
                setattr(self, key, value)
    
        def __repr__(self):
            s = super().__repr__()[1:-1]
            for key, val in self.__dict__.items():
                s += ', '+key+'='+repr(val)
            return 'struct('+s+')'
            
        def __str__(self):
            s = super().__str__()[1:-1]
            print('Debug : super().__str__() = "'+super().__str__()+'"')
            print('Debug : list(self).__str__() = "'+list(self).__str__()+'"')
            print('Debug : s = "'+s+'"')
            for key, val in self.__dict__.items():
                s += ', '+key+'='+str(val)
            return '{'+s+'}'

    a = struct(1, 2, 3, a="akeja", b=21, c=True, d="lkj")
    print('repr(a)="'+repr(a)+'"\n')
    print('str(a)="'+str(a)+'"\n')

Executing this code in idle-3.5.2 will yield the following result :

    >>> 
     RESTART: struct.py 
    repr(a)="struct(1, 2, 3, b=21, d='lkj', a='akeja', c=True)"
    
    Debug : super().__str__() = "struct(1, 2, 3, b=21, d='lkj', a='akeja', c=True)"
    Debug : list(self).__str__() = "[1, 2, 3]"
    Debug : s = "truct(1, 2, 3, b=21, d='lkj', a='akeja', c=True"
    str(a)="{truct(1, 2, 3, b=21, d='lkj', a='akeja', c=True, b=21, d=lkj, a=akeja, c=True}"
    
    >>> 

As one can see in the second debug lines, the call to `super().__str__()` which I expect to return the result from a call to the `__str__` function from my super class (`list`), will in fact return something which looks very much like the expected return from `self.__repr__()`

It seems that `super().__str__()` calls `self.__repr__()` instead of `list(self).__str__()` or even `super().__repr__()`.

----------
components: Interpreter Core
messages: 329331
nosy: Camion
priority: normal
severity: normal
status: open
title: Calling for super().__str__ seems to call self.__repr__ in list subclass
type: behavior
versions: Python 3.5

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35174>
_______________________________________