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Function Transformations

"Function transformation" is just a concise way to describe a specific type of higher-order function. It's when a function takes a function (or functions) as input and returns a new function. Let's look at an example:

from collections.abc import Callable

def multiply(x: int, y: int) -> int:
    return x * y

def add(x: int, y: int) -> int:
    return x + y

# self_math is a higher-order function
# input: a function that takes two arguments and returns a value
# output: a new function that takes one argument and returns a value
def self_math(math_func: Callable[[int, int], int]) -> Callable[[int], int]:
    def inner_func(x: int) -> int:
        return math_func(x, x)
    return inner_func

square_func: Callable[[int], int] = self_math(multiply)
double_func: Callable[[int], int] = self_math(add)

print(square_func(5))
# prints 25

print(double_func(5))
# prints 10

The self_math function takes a function that operates on two different parameters (e.g. multiply or add) and returns a new function that operates on one parameter twice (e.g. square or double).

Assignment

Doc2Doc needs a good logging system so that users and developers alike can see what's going on under the hood. Complete the get_logger function.

It takes a formatter function as a parameter and returns a new function. Steps:

Define a new function, logger, inside get_logger (see self_math above as an example). It accepts two strings. You can just name them first and second if you like.
The logger function should not return anything. It should simply print the result of calling the given formatter function with the first and second strings as arguments.
Return the new logger function.

Tip

The colon_delimit and dash_delimit functions are "formatters" that will be passed into our get_logger function by the tests. You don't need to touch them, but it's important to understand that when you call formatter() in the get_logger function, you're calling one of these functions.