map, filter & lambda

A lambda is a tiny unnamed function: lambda n: n * 2. It is limited to one expression.

map(function, items) applies a function to every item. filter(function, items) keeps items where the function returns true.
Both return lazy iterators, so wrap them in list() to see the results. A comprehension is often clearer for simple cases.

nums = [1, 2, 3, 4]
doubled = list(map(lambda n: n * 2, nums))
print(doubled)