[Python-checkins] Minor improvements to the convolve() recipe (GH-24012)

[rhettinger]

https://github.com/python/cpython/commit/f421bfce80730cb0ff5cbe14727ac30cf0462eed
commit: f421bfce80730cb0ff5cbe14727ac30cf0462eed
branch: master
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: rhettinger <rhettinger at users.noreply.github.com>
date: 2020-12-30T12:51:19-08:00
summary:

Minor improvements to the convolve() recipe (GH-24012)

* Minor improvement to speed and space efficiency for the convolve() recipe
* Don't require convolve's kernel to be a sequence.

files:
M Doc/library/itertools.rst

diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 03416a0a7fbcb..fd77f99a88f57 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -791,9 +791,9 @@ which incur interpreter overhead.
        # convolve(data, [0.25, 0.25, 0.25, 0.25]) --> Moving average (blur)
        # convolve(data, [1, -1]) --> 1st finite difference (1st derivative)
        # convolve(data, [1, -2, 1]) --> 2nd finite difference (2nd derivative)
-       kernel = list(reversed(kernel))
+       kernel = tuple(kernel)[::-1]
        n = len(kernel)
-       window = collections.deque([0] * n, maxlen=n)
+       window = collections.deque([0], maxlen=n) * n
        for x in chain(signal, repeat(0, n-1)):
            window.append(x)
            yield sum(map(operator.mul, kernel, window))