Is there a way to auto generate a __str__() implementation in python?

Question

Being tired manually implementing a string representation for my classes, I was wondering if there is a pythonic way to do that automatically.

I would like to have an output that covers all the attributes of the class and the class name. Here is an example:

class Foo(object):
    attribute_1 = None
    attribute_2 = None
    def __init__(self, value_1, value_2):
         self.attribute_1 = value_1
         self.attribute_2 = value_2

Resulting in:

bar = Foo("baz", "ping")
print(str(bar)) # desired: Foo(attribute_1=baz, attribute_2=ping)

This question came to mind after using Project Lombok @ToString in some Java projects.

Answer 1

You can iterate instance attributes using vars, dir, ...:

def auto_str(cls):
    def __str__(self):
        return '%s(%s)' % (
            type(self).__name__,
            ', '.join('%s=%s' % item for item in vars(self).items())
        )
    cls.__str__ = __str__
    return cls

@auto_str
class Foo(object):
    def __init__(self, value_1, value_2):
        self.attribute_1 = value_1
        self.attribute_2 = value_2

Applied:

>>> str(Foo('bar', 'ping'))
'Foo(attribute_2=ping, attribute_1=bar)'