CODEWITHSUNDEEP
python
user69818
user69818

Reputation: 403

Is it possible to dynamically create functions/variables in a module?

Say, I have a general function f(input, kind) and a long list of kind. I would like to create functions f_kind(input) for each kind in the list. Instead of doing it manually by f_kind1 = partial(f, kind=kind1), is it possible to create them more dynamically via a loop over the list (something similar to setattr(class_name, method_name, method) inside a class)?

Upvotes: 0

Views: 50

Answers (1)

martineau
martineau

Reputation: 123463

Your question reminded by of an article I read long ago by Guido van Rossum about implementing multimethods in Python — because at it's core, that's what you're doing.

It would need to be adapted to work on a class, but I think it might be a better approach than using setattr() to achieve your goal.

mm.py:

''' MultiMethod module. '''

_registry = {}

class MultiMethod(object):
    def __init__(self, name):
        self.name = name
        self.typemap = {}

    def __call__(self, *args):
        types = tuple(arg.__class__ for arg in args)
        function = self.typemap.get(types)
        if function is None:
            raise TypeError("no match")
        return function(*args)

    def register(self, types, function):
        if types in self.typemap:
            raise TypeError("duplicate registration")
        print('registering: {!r} for args: {}'.format(function.__name__, types))
        self.typemap[types] = function

def multimethod(*types):
    def register(function):
        name = function.__name__
        mm = _registry.get(name)
        if mm is None:
            mm = _registry[name] = MultiMethod(name)
        mm.register(types, function)
        return mm

    return register

Sample usage.

mm_test.py:

from mm import multimethod

@multimethod(int)
def f(input):
    print('f_{}({!r}) called'.format(type(input).__name__, input))


@multimethod(str)
def f(input):
    print('f_{}({!r}) called'.format(type(input).__name__, input))

f('answer')
f(42)

@multimethod(float)
def f(input):
    print('f_{}({!r}) called'.format(type(input).__name__, input))

f(3.141529)

Output:

registering: 'f' for args: (<class 'int'>,)
registering: 'f' for args: (<class 'str'>,)
f_str('answer') called
f_int(42) called
registering: 'f' for args: (<class 'float'>,)
f_float(3.141529) called

Upvotes: 1

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