Custom higher-order functions

Functions like sort, max, or min can take arguments like key= that are functions and can determine their behavior. This makes the built-in functions sort and max way more powerful and generic. They can be used in many more scenarios than if they would only compare the values themselves without the key= argument.

We can create our own higher-order functions as well:

def modify(numbers, f):
    res = [f(n) for n in numbers]
    return res

print(modify([1, 2, 3], lambda x: x**2))   # [1, 4, 9]
print(modify([1, 2, 3], lambda x: -x))     # [-1, -2, -3]
print(modify([2, 0, 1], lambda x: 2 * x))  # [4, 0, 2]
print(modify([2, 0, 1], str))              # ['2', '0', '1']

Here we pass different functions as f to the higher-order function modify. The modify function creates a new list from the input one and returns the result. Note that we can even pass a function like str to the function as well. So, each element of the input list will get applied a str() function - str(2), str(0), str(1).

Challenge

Implement a generic version of the sum function called generic_sum which will take a collection as the first argument (it can be a list, a set, or a list of tuples) and a function as a second argument that obtains a number from each element of the collection.

def generic_sum():
    ...

print(generic_sum([1, 2, 3], lambda x: x))                   # 6
print(generic_sum({1, 2, 3}, lambda x: x))                   # 6
print(generic_sum([(1, 3), (4, 6)], lambda x: x[0] + x[1]))  # 14

Challenge

Constraints

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