From 9f0af71f948cd3d1a61d05b6a5355a886c7a1373 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Fri, 3 May 2024 17:07:47 -0500 Subject: [PATCH] Minor improvements to the itertools recipes (GH-118563) (cherry picked from commit 6d9e8e989e9e0931f84155451f921621b906e213) Co-authored-by: Raymond Hettinger --- Doc/library/itertools.rst | 36 ++++++++++++------------------------ 1 file changed, 12 insertions(+), 24 deletions(-) diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index 8bb9b65203f0ed..e3ce72a2f36140 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -818,10 +818,7 @@ and :term:`generators ` which incur interpreter overhead. return map(function, count(start)) def repeatfunc(func, times=None, *args): - """Repeat calls to func with specified arguments. - - Example: repeatfunc(random.random) - """ + "Repeat calls to func with specified arguments." if times is None: return starmap(func, repeat(args)) return starmap(func, repeat(args, times)) @@ -843,10 +840,8 @@ and :term:`generators ` which incur interpreter overhead. "Advance the iterator n-steps ahead. If n is None, consume entirely." # Use functions that consume iterators at C speed. if n is None: - # feed the entire iterator into a zero-length deque collections.deque(iterator, maxlen=0) else: - # advance to the empty slice starting at position n next(islice(iterator, n, n), None) def nth(iterable, n, default=None): @@ -865,7 +860,7 @@ and :term:`generators ` which incur interpreter overhead. def all_equal(iterable, key=None): "Returns True if all the elements are equal to each other." - # all_equal('4٤໔４৪', key=int) → True + # all_equal('4٤௪౪໔', key=int) → True return len(take(2, groupby(iterable, key))) <= 1 def unique_justseen(iterable, key=None): @@ -895,9 +890,9 @@ and :term:`generators ` which incur interpreter overhead. def sliding_window(iterable, n): "Collect data into overlapping fixed-length chunks or blocks." # sliding_window('ABCDEFG', 4) → ABCD BCDE CDEF DEFG - it = iter(iterable) - window = collections.deque(islice(it, n-1), maxlen=n) - for x in it: + iterator = iter(iterable) + window = collections.deque(islice(iterator, n - 1), maxlen=n) + for x in iterator: window.append(x) yield tuple(window) @@ -947,8 +942,8 @@ and :term:`generators ` which incur interpreter overhead. seq_index = getattr(iterable, 'index', None) if seq_index is None: # Path for general iterables - it = islice(iterable, start, stop) - for i, element in enumerate(it, start): + iterator = islice(iterable, start, stop) + for i, element in enumerate(iterator, start): if element is value or element == value: yield i else: @@ -963,10 +958,7 @@ and :term:`generators ` which incur interpreter overhead. pass def iter_except(func, exception, first=None): - """ Call a function repeatedly until an exception is raised. - - Converts a call-until-exception interface to an iterator interface. - """ + "Convert a call-until-exception interface to an iterator interface." # iter_except(d.popitem, KeyError) → non-blocking dictionary iterator try: if first is not None: @@ -1066,14 +1058,10 @@ The following recipes have a more mathematical flavor: # sieve(30) → 2 3 5 7 11 13 17 19 23 29 if n > 2: yield 2 - start = 3 data = bytearray((0, 1)) * (n // 2) - limit = math.isqrt(n) + 1 - for p in iter_index(data, 1, start, limit): - yield from iter_index(data, 1, start, p*p) + for p in iter_index(data, 1, start=3, stop=math.isqrt(n) + 1): data[p*p : n : p+p] = bytes(len(range(p*p, n, p+p))) - start = p*p - yield from iter_index(data, 1, start) + yield from iter_index(data, 1, start=3) def factor(n): "Prime factors of n." @@ -1093,8 +1081,8 @@ The following recipes have a more mathematical flavor: "Count of natural numbers up to n that are coprime to n." # https://mathworld.wolfram.com/TotientFunction.html # totient(12) → 4 because len([1, 5, 7, 11]) == 4 - for p in unique_justseen(factor(n)): - n -= n // p + for prime in set(factor(n)): + n -= n // prime return n