Python: How to add str for functions

Question

When I printed my function (without the function call),

def loss(y_true, y_pred): 
    return backend.sum(backend.abs(y_true - y_pred))

I got something like

<function __main__.loss>

I need it to return a string like

Absolute Error Sum

Most links I looked at explain how to do the same for class objects. How do I define what string the function should return?

Are you sure you it to return that string? That is the sort of info that usually goes in a docstring. — Robᵩ, Mar 24 '18 at 01:14
Yes, convert it to a class. Implement `__call__` method to make the instance callable, override `__repr__` to customize the output. — kindall, Mar 24 '18 at 01:25

Viknesh · Accepted Answer · 2018-03-26T08:06:38.713

1

You should be able to edit the __name__ attribute of it:

>>> def f(x): print(x)

>>> f
<function f at 0x7feb2c843a28>

>>> f.__name__ = 'my function'

>>> f
<function my function at 0x7feb2c843a28>

>>> f.__name__
my function

Edit: note that in Python 3, you may have to overwrite the __qualname__ property instead (see https://www.python.org/dev/peps/pep-3155/ and https://github.com/ipython/ipython/issues/5566/).

edited Mar 26 '18 at 08:06

answered Mar 24 '18 at 01:13

Viknesh

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but if i need to import this function to many other files, how do I do it? – Saravanabalagi Ramachandran Mar 24 '18 at 01:23
is it possible to edit this attribute inside of the function itself using something like `self.__name__ == mystr`??? – Saravanabalagi Ramachandran Mar 24 '18 at 01:27
I don't think it will be possible to edit the name within the definition of the function itself. However, if you put the `__name__` definition at the same place that the function is defined, it should run whenever the function is imported. – Viknesh Mar 24 '18 at 01:35
unfortunately that didn't work. works as long as I'm doing that in the current file – Saravanabalagi Ramachandran Mar 24 '18 at 01:50
If you're using Python 3, you will have to use `__qualname__` instead (see https://github.com/ipython/ipython/issues/5566/) – Viknesh Mar 26 '18 at 08:04

score 0 · Answer 2 · answered Mar 24 '18 at 01:14

You can't customize the default repr of the function type, but you can extract the part you care about and format it however you want.

For example, if you want a friendlier name, the actual name is stored in __name__, so you could print(loss.__name__) if you want to avoid the extra wrapping. This isn't perfect (lambda functions don't have names for instance), but it's better than trying to rewrite the default repr for functions.

Python: How to add __str__ for functions

2 Answers2

Python: How to add str for functions