creating a partial-like object with dynamic arguments

Question

I'm trying to create a partial function but with dynamic arguments that are stored as class attributes and changed accordingly. Something like the following code:

from functools import partial

def foo(*args, msg):
    print(msg)

class Bar:
    def __init__(self, msg):
        self.msg = msg
        self.functions = dict()
        self.functions['foo'] = partial(foo, msg=self.msg)

    def foo_method(self, *args):
        return self.functions['foo'](*args)

b =Bar('1')
b.foo_method()
b.msg = '2'
b.foo_method()

Only, of course, both statements will print '1' as the partial object fixes the arguments. The only alternative I found was changing the attribute to a property and manually changing the partial attributes with the setter:

class Bar:
    def __init__(self, msg):
        self._msg = None
        self.functions = dict()
        self.functions['foo'] = partial(foo)
        self.msg = msg

    def foo_method(self, *args):
        return self.functions['foo'](*args)

    @property
    def msg(self):
        return self._msg

    @msg.setter
    def msg(self, msg):
        self._msg = msg
        self.functions['foo'].keywords['msg'] = msg

I would like to know if there is a more "pythonic" / efficient way to do this, since I really don't need to use properties except for this workaround.

Answer 1

You can use lambda instead of partial for deferred (or often referred to as "lazy") evaluation of the arguments, so that self.msg is not evaluated until the function is called:

class Bar:
    def __init__(self, msg):
        self.msg = msg
        self.functions = dict()
        self.functions['foo'] = lambda *args: foo(*args, msg=self.msg)

    def foo_method(self, *args):
        return self.functions['foo'](*args)

Answer 2

What's wrong with just storing a reference to the passed function and constructing the call on the spot? i.e.:

class Bar:

    def __init__(self, msg):
        self.msg = msg
        self.foo = foo  # a reference to foo, not needed here but used as an example

    def foo_method(self, *args):
        return self.foo(*args, msg=self.msg)  # or just: foo(*args, msg=self.msg)