Question

I’ve only seen examples for setting the __repr__ method in class definitions. Is it possible to change the __repr__ for functions either in their definitions or after defining them?

I’ve attempted without success…

>>> def f():
    pass
>>> f
<function f at 0x1026730c8>
>>> f.__repr__ = lambda: '<New repr>'
>>> f
<function __main__.f>

Answer 1

Yes, if you’re willing to forgo the function actually being a function.

First, define a class for our new type:

import functools
class reprwrapper(object):
    def __init__(self, repr, func):
        self._repr = repr
        self._func = func
        functools.update_wrapper(self, func)
    def __call__(self, *args, **kw):
        return self._func(*args, **kw)
    def __repr__(self):
        return self._repr(self._func)

Add in a decorator function:

def withrepr(reprfun):
    def _wrap(func):
        return reprwrapper(reprfun, func)
    return _wrap

And now we can define the repr along with the function:

@withrepr(lambda x: "<Func: %s>" % x.__name__)
def mul42(y):
    return y*42

Now repr(mul42) produces '<Func: mul42>'