使用Python fn模块的函数

Question

I found this functional programming library fn and I found the following code for function currying

>>> from fn.func import curried
>>> @curried
... def sum5(a, b, c, d, e):
...     return a + b + c + d + e
...
>>> sum5(1)(2)(3)(4)(5)
15
>>> sum5(1, 2, 3)(4, 5)
15

but when I run it I get

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/adrian/.local/lib/python2.7/site-packages/fn/func.py", line 83, in _curried
    return curried(partial(func, *args, **kwargs))
  File "/home/adrian/.local/lib/python2.7/site-packages/fn/func.py", line 69, in curried
    @wraps(func)
  File "/usr/lib/python2.7/functools.py", line 33, in update_wrapper
    setattr(wrapper, attr, getattr(wrapped, attr))
AttributeError: 'functools.partial' object has no attribute '__module__'

Is it possible to solve this?

Answer 1

wraps behaviour is different in python3 compared to python2 in particular `update_wrapper``, the code will work with python3 as is but you would need to use the wraps implementation from py3 for the it to work.

I would file a bug report but in the mean time the relevant functions from functools are here:

from functools import wraps, partial, WRAPPER_ASSIGNMENTS,WRAPPER_UPDATES
def update_wrapper(wrapper,
                   wrapped,
                   assigned = WRAPPER_ASSIGNMENTS,
                   updated = WRAPPER_UPDATES):
    """Update a wrapper function to look like the wrapped function
       wrapper is the function to be updated
       wrapped is the original function
       assigned is a tuple naming the attributes assigned directly
       from the wrapped function to the wrapper function (defaults to
       functools.WRAPPER_ASSIGNMENTS)
       updated is a tuple naming the attributes of the wrapper that
       are updated with the corresponding attribute from the wrapped
       function (defaults to functools.WRAPPER_UPDATES)
    """
    for attr in assigned:
        try:
            value = getattr(wrapped, attr)
        except AttributeError:
            pass
        else:
            setattr(wrapper, attr, value)
    for attr in updated:
        getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
    # Issue #17482: set __wrapped__ last so we don't inadvertently copy it
    # from the wrapped function when updating __dict__
    wrapper.__wrapped__ = wrapped
    # Return the wrapper so this can be used as a decorator via partial()
    return wrapper

def wraps(wrapped,
          assigned = WRAPPER_ASSIGNMENTS,
          updated = WRAPPER_UPDATES):
    """Decorator factory to apply update_wrapper() to a wrapper function
       Returns a decorator that invokes update_wrapper() with the decorated
       function as the wrapper argument and the arguments to wraps() as the
       remaining arguments. Default arguments are as for update_wrapper().
       This is a convenience function to simplify applying partial() to
       update_wrapper().
    """
    return partial(update_wrapper, wrapped=wrapped,
                   assigned=assigned, updated=updated)

The curried wrapper:

def curried(func):
    """A decorator that makes the function curried
    Usage example:
    >>> @curried
    ... def sum5(a, b, c, d, e):
    ...     return a + b + c + d + e
    ...
    >>> sum5(1)(2)(3)(4)(5)
    15
    >>> sum5(1, 2, 3)(4, 5)
    15
    """
    @wraps(func)
    def _curried(*args, **kwargs):
        f = func
        count = 0
        while isinstance(f, partial):
            print(f)
            if f.args:
                count += len(f.args)
            f = f.func

        spec = getargspec(f)

        if count == len(spec.args) - len(args):
            return func(*args, **kwargs)

        return curried(partial(func, *args, **kwargs))
    return _curried

To fix just the curried function for python2 you could only keep attrs from WRAPPER_ASSIGNMENTS that the func has:

#change this line 

@wraps(func, (attr for attr in WRAPPER_ASSIGNMENTS if hasattr(func, attr)))
    def _curried(*args, **kwargs):
        f = func
        count = 0
        while isinstance(f, partial):
            print(f)
            if f.args:
                count += len(f.args)
            f = f.func

        spec = getargspec(f)

        if count == len(spec.args) - len(args):
            return func(*args, **kwargs)

        return curried(partial(func, *args, **kwargs))
    return _curried

Answer 2

Maybe you want to have a look at functools.partial . You can get rid of the annotation and just use

curried = partial(sum5, 2, 3, 4)
curried(5, 6)