How to pass an unspecified number of arguments into lambda? (in Python)

Question

Say we have a function func and in that function there's a list of n items. The n number changes depending on the argument(s) given to func. There's also a lambda function in func (created with eval any time func is called) that takes n number of arguments and returns something. Is there any way you could pass the items from the list to the lambda function (items from the list and arguments in lambda are always equal to each other in number, the only difference is that list items are wrapped in [] and arguments are not)? You can't simply insert the list into lambda since it sees it as one argument when in fact the list might have 3, 30 or any number of arguments. A simplified picture:

def func(*args):
    lst = [n items where n changes depending on *args]
    lambda n arguments/items: do sth

why are you using a lambda in the first place, what are you trying to do? — Padraic Cunningham
– Padraic Cunningham, Commented Dec 10, 2014 at 22:21

Greg · Accepted Answer · 2014-12-10 22:20:42Z

7

You can do something similar to *arg and **kwargs with lambda:

>>> a = lambda *args, **kwargs: (args, kwargs)
>>> a(1, 2, a="a", b="b")
((1, 2), {'a': 'a', 'b': 'b'})

answered Dec 10, 2014 at 22:20

Greg

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3 Comments

Mariusz Over a year ago

But my lambda function is already created and it looks for example like this: lambda x,y,z: z*100 + x - y. So is my list and it looks like this: lst = [4,5,6]. The question is how to pass SPECIFIC items from the list into lambda function (knowing only that the number of items and the number of arguments is the same). If there's no way of doing it.. fine. I'd just like to know that for sure :)

ch3ka Over a year ago

is my_lambda_func(*lst) what you are looking for?

Mariusz Over a year ago

cool, I thought that '*' symbol only allows for many arguments to be passed to a function, but it can actually 'unpack' a list and serve its items as arguments. Thx! It worked.

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