def test_order(self):
"Test that composed functions work in the correct order."
filter_fives = partial(filter, lambda x: x != 5)
# complicated function that only works if it's applied correctly.
function = compose(lambda x: x - 1, lambda x: x*2, sum, filter_fives)
# the proper order of things:
# * filter out the fives. [5, 3, 1] -> [3, 1]
# * sum the items of the list. [3, 1] -> 4
# * multiply by two. 4 -> 8
# * subtract one. 8 -> 7
self.assertEqual(function([5, 3, 1]), 7)
def test_basic(self):
"""A trivial example for composition; sum numbers that are not 5.
This is not the most pythonic way to do it, but it makes for a good
example of function composition.
"""
# a function that returns a list without any fives.
filter_fives = partial(filter, lambda x: x != 5)
# a function that sums the result of filter_fives on a list.
function = compose(sum, filter_fives)
# for each of these cases, check that we get the expected result.
cases = [
([1, 2, 3, 4, 5], 10),
([5, 5], 0),
([10, 15, 5], 25),
]
for input, output in cases:
self.assertEqual(function(input), output)
def test_multiple(self):
"Test whether we can compose more than one function."
# basically, add 3 to the sum of a list.
function = compose(lambda x: x + 1, lambda x: x + 2, sum)
self.assertEqual(function([5, 3]), 11)
