Guido said it would cause too much disturbance…

Python has two ways to convert an object to a string: str(x) and repr(x). str is supposed to be user-readable, and repr is more technical, e.g. for debugging purposes.

To my surprise, if I have a list of things, str(list) and repr(list) do the same thing and include a repr of each item. I would expect str(list) to include str of the list items, and repr(list) to include repr of the items.

Apparently, I am not alone: back in 2008 this was proposed by Oleg Broytman and Jim J. Jewett (PEP 3140), but rejected, because “Guido said it would cause too much disturbance too close to Beta“. It is causing disturbance ever since, I suppose…


class Foo:
    def __init__(self, x):
        self.x = x
    def __str__(self):
        return f'Foo with {self.x}'
    def __repr__(self):
        return f'Foo({repr(self.x)})'
foo = Foo(42)    
print(repr(foo))           # Foo(42)
print(str(foo))            # Foo with 42

lst = [Foo(1), Foo(2)]
print(repr(lst))           # [Foo(1), Foo(2)]
print(str(lst))            # [Foo(1), Foo(2)]
# One would expect that str() of list calls str() for each item, but it doesn't it calls repr() instead

Leave a Reply

Your email address will not be published. Required fields are marked *