From 6bde3d2fd323fde8b9abf19b996ef7e8f1c549c1 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Fri, 13 Jan 2023 19:01:22 -0600 Subject: [PATCH] Add recipes to showcase tee(), zip*, batched, starmap, and product. (GH-101023) --- Doc/library/itertools.rst | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index e7d2e13626f..8d83d92660d 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -838,6 +838,22 @@ which incur interpreter overhead. "Returns the sequence elements n times" return chain.from_iterable(repeat(tuple(iterable), n)) + def sum_of_squares(it): + "Add up the squares of the input values." + # sum_of_squares([10, 20, 30]) -> 1400 + return math.sumprod(*tee(it)) + + def transpose(it): + "Swap the rows and columns of the input." + # transpose([(1, 2, 3), (11, 22, 33)]) --> (1, 11) (2, 22) (3, 33) + return zip(*it, strict=True) + + def matmul(m1, m2): + "Multiply two matrices." + # matmul([(7, 5), (3, 5)], [[2, 5], [7, 9]]) --> (49, 80), (41, 60) + n = len(m2[0]) + return batched(starmap(math.sumprod, product(m1, transpose(m2))), n) + def convolve(signal, kernel): # See: https://betterexplained.com/articles/intuitive-convolution/ # convolve(data, [0.25, 0.25, 0.25, 0.25]) --> Moving average (blur) @@ -1207,6 +1223,17 @@ which incur interpreter overhead. >>> list(ncycles('abc', 3)) ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c'] + >>> sum_of_squares([10, 20, 30]) + 1400 + + >>> list(transpose([(1, 2, 3), (11, 22, 33)])) + [(1, 11), (2, 22), (3, 33)] + + >>> list(matmul([(7, 5), (3, 5)], [[2, 5], [7, 9]])) + [(49, 80), (41, 60)] + >>> list(matmul([[2, 5], [7, 9], [3, 4]], [[7, 11, 5, 4, 9], [3, 5, 2, 6, 3]])) + [(29, 47, 20, 38, 33), (76, 122, 53, 82, 90), (33, 53, 23, 36, 39)] + >>> data = [20, 40, 24, 32, 20, 28, 16] >>> list(convolve(data, [0.25, 0.25, 0.25, 0.25])) [5.0, 15.0, 21.0, 29.0, 29.0, 26.0, 24.0, 16.0, 11.0, 4.0] -- 2.39.2