Functions as values in Python

Functions are objects: pass them, store them, return them.

def apply_twice(fn, value):
    return fn(fn(value))


def add_five(n):
    return n + 5


result = apply_twice(add_five, 10)

celsius = [0, 20, 37, 100]
fahrenheit = list(map(lambda c: c * 9 / 5 + 32, celsius))
warm = list(filter(lambda c: c > 15, celsius))

operations = {"double": lambda n: n * 2, "square": lambda n: n * n}
answer = operations["square"](12)

How it works

1. apply_twice receives a function and calls it twice.
2. map and filter transform lists with lambdas.
3. A dict of lambdas dispatches operations by name.

Keywords and builtins used here

• add_five
• apply_twice
• def
• filter
• lambda
• list
• map
• return

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Step 4 of 6 in Functions, step 36 of 72 in Language basics.

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