Possible to change a function's repr in python?
Yes, if you're willing to forgo the function actually being a function.
First, define a class for our new type:
import functoolsclass 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>'
In order to do that, you'd need to change the __repr__
function for the given class, which in this case is the built-in function class (types.FunctionType
). Since in Python you cannot edit built-in classes, only subclass them, you cannot.
However, there are two approaches you could follow:
- Wrap some functions as kwatford suggested
Create your own representation protocol with your own repr function. For example, you could define a
myrepr
function that looks for__myrepr__
methods first, which you cannot add to the function class but you can add it to individual function objects as you suggest (as well as your custom classes and objects), then defaults to repr if__myrepr__
is not found. A possible implementation for this would be:def myrepr(x): try: x.__myrepr__ except AttributeError: return repr(x) else: return x.__myrepr__()
Then you could define
__myrepr__
methods and use themyrepr
function. Alternatively, you could also do__builtins__.repr = myrepr
to make your function the defaultrepr
and keep usingrepr
. This approach would end up doing exactly what you want, though editing__builtins__
may not always be desirable.