30-seconds-of-code/snippets/when.md

title, tags, expertise, firstSeen, lastUpdated

title	tags	expertise	firstSeen	lastUpdated
Apply function when true	function	intermediate	2020-01-02T20:25:45+02:00	2020-11-09T23:56:11+02:00

Tests a value, x, against a testing function, conditionally applying a function.

• Check if the value of predicate() is True for x and if so call when_true(), otherwise return x.

def when(predicate, when_true):
  return lambda x: when_true(x) if predicate(x) else x

double_even_numbers = when(lambda x: x % 2 == 0, lambda x : x * 2)
double_even_numbers(2) # 4
double_even_numbers(1) # 1