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@JulienPalard
Created August 1, 2014 10:51
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KISS Python curry
#!/usr/bin/env python
def curry(func):
"""
Decorator to curry a function, typical usage:
>>> @curry
... def foo(a, b, c):
... return a + b + c
The function still work normally:
>>> foo(1, 2, 3)
6
And in various curried forms:
>>> foo(1)(2, 3)
6
>>> foo(1)(2)(3)
6
This also work with named arguments:
>>> foo(a=1)(b=2)(c=3)
6
>>> foo(b=1)(c=2)(a=3)
6
>>> foo(a=1, b=2)(c=3)
6
>>> foo(a=1)(b=2, c=3)
6
And you may also change your mind on named arguments,
But I don't know why you may want to do that:
>>> foo(a=1, b=0)(b=2, c=3)
6
Finally, if you give more parameters than expected, the exception
is the expected one, not some garbage produced by the currying
mechanism:
>>> foo(1, 2)(3, 4)
Traceback (most recent call last):
...
TypeError: foo() takes exactly 3 arguments (4 given)
"""
def curried(*args, **kwargs):
if len(args) + len(kwargs) >= func.__code__.co_argcount:
return func(*args, **kwargs)
return (lambda *args2, **kwargs2:
curried(*(args + args2), **dict(kwargs, **kwargs2)))
return curried
if __name__ == "__main__":
import doctest
doctest.testmod()
@blurrcat
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blurrcat commented Dec 5, 2016

Fantastic! Thanks!

You may use functools.wraps to make the intermediate curried functions look like the original function.

from functools import wraps

def curry(func):
    """
    >>> @curry
    ... def foo(a, b, c):
    ...     return a + b + c
    >>> foo(1)
    <function __main__.foo>
    """
    @wraps(func)
    def curried(*args, **kwargs):
        if len(args) + len(kwargs) >= func.__code__.co_argcount:
            return func(*args, **kwargs)

        @wraps(func)
        def new_curried(*args2, **kwargs2):
            return curried(*(args + args2), **dict(kwargs, **kwargs2))

        return new_curried

    return curried

Now instead of showing <function __main__.curry.<locals>.curried.<locals>.<lambda>> for foo(1), we have the expected representation of the function. This can make debugging easier.

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