Python __repr__ for all member variables

Question

Implementing __repr__ for a class Foo with member variables x and y, is there a way to automatically populate the string? Example that does not work:

class Foo(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Foo({})".format(**self.__dict__)

>>> foo = Foo(42, 66)
>>> print(foo)
IndexError: tuple index out of range

And another:

from pprint import pprint
class Foo(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Foo({})".format(pprint(self.__dict__))

>>> foo = Foo(42, 66)
>>> print(foo)
{'x': 42, 'y': 66}
Foo(None)

Yes I could define the method as

    def __repr__(self):
        return "Foo({x={}, y={}})".format(self.x, self.x)

but this gets tedious when there are many member variables.

Answer 1

I use this as a mixin when I want something like that:

class SimpleRepr(object):
    """A mixin implementing a simple __repr__."""
    def __repr__(self):
        return "<{klass} @{id:x} {attrs}>".format(
            klass=self.__class__.__name__,
            id=id(self) & 0xFFFFFF,
            attrs=" ".join("{}={!r}".format(k, v) for k, v in self.__dict__.items()),
            )

It gives the class name, the (shortened) id, and all of the attributes.

Answer 2

I think you want something like this:

    def __repr__(self):
        return "Foo({!r})".format(self.__dict__)

---

This will add repr(self.__dict__) in the string, using !r in a format specifier tells format() to call the item's __repr__().

See the "Conversion field" here: https://docs.python.org/3/library/string.html#format-string-syntax

---

Based on Ned Batchelder's answer, you can replace the line above by

return "{}({!r})".format(self.__class__.__name__, self.__dict__)

for a more generic approach.