How can I customize the string representation of Python classes using metaclasses?

Custom String Representation for Classes: A Pythonic Approach

In Python, defining your own string representation for classes can offer greater control over how the class is presented. Unlike the default representation that resembles <class '__main__.foo'>, you might want to create a more informative or visually appealing display. This article explores how to tailor the string representation of classes using metaclasses.

Consider the following class:

class foo(object):
    pass

By default, converting foo to a string yields:

>>> str(foo)
"<class '__main__.foo'>"

To customize this representation, you can implement either __str__() or __repr__() within the class's metaclass. These magic methods are responsible for returning the readable and unambiguous string representations of the class, respectively.

The following example demonstrates how to implement a custom __repr__() in a metaclass:

class MC(type):
    def __repr__(self):
        return 'Wahaha!'

class C(object):
    __metaclass__ = MC


print(C)

This code will output "Wahaha!" when you print the class C.

If you desire a readable stringification, use __str__; for unambiguous representations, use __repr__. Python 3 requires you to specify the metaclass in the class definition itself, like so:

class MC(type):
    def __repr__(self):
        return 'Wahaha!'

class C(object, metaclass=MC):
    pass


print(C)

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