Minor readability improvements for the itertools recipes (gh-127928)

Author: rhettinger

Doc/library/itertools.rst

@@ -30,11 +30,6 @@ For instance, SML provides a tabulation tool: ``tabulate(f)`` which produces a
 sequence ``f(0), f(1), ...``.  The same effect can be achieved in Python
 by combining :func:`map` and :func:`count` to form ``map(f, count())``.
 
-These tools and their built-in counterparts also work well with the high-speed
-functions in the :mod:`operator` module.  For example, the multiplication
-operator can be mapped across two vectors to form an efficient dot-product:
-``sum(starmap(operator.mul, zip(vec1, vec2, strict=True)))``.
-
 
 **Infinite iterators:**
 
@@ -843,12 +838,11 @@ and :term:`generators <generator>` which incur interpreter overhead.
 
 .. testcode::
 
-   import collections
-   import contextlib
-   import functools
-   import math
-   import operator
-   import random
+   from collections import deque
+   from contextlib import suppress
+   from functools import reduce
+   from math import sumprod, isqrt
+   from operator import itemgetter, getitem, mul, neg
 
    def take(n, iterable):
        "Return first n items of the iterable as a list."
@@ -863,11 +857,11 @@ and :term:`generators <generator>` which incur interpreter overhead.
        "Return function(0), function(1), ..."
        return map(function, count(start))
 
-   def repeatfunc(func, times=None, *args):
-       "Repeat calls to func with specified arguments."
+   def repeatfunc(function, times=None, *args):
+       "Repeat calls to a function with specified arguments."
        if times is None:
-           return starmap(func, repeat(args))
-       return starmap(func, repeat(args, times))
+           return starmap(function, repeat(args))
+       return starmap(function, repeat(args, times))
 
    def flatten(list_of_lists):
        "Flatten one level of nesting."
@@ -885,13 +879,13 @@ and :term:`generators <generator>` which incur interpreter overhead.
    def tail(n, iterable):
        "Return an iterator over the last n items."
        # tail(3, 'ABCDEFG') → E F G
-       return iter(collections.deque(iterable, maxlen=n))
+       return iter(deque(iterable, maxlen=n))
 
    def consume(iterator, n=None):
        "Advance the iterator n-steps ahead. If n is None, consume entirely."
        # Use functions that consume iterators at C speed.
        if n is None:
-           collections.deque(iterator, maxlen=0)
+           deque(iterator, maxlen=0)
        else:
            next(islice(iterator, n, n), None)
 
@@ -919,8 +913,8 @@ and :term:`generators <generator>` which incur interpreter overhead.
        # unique_justseen('AAAABBBCCDAABBB') → A B C D A B
        # unique_justseen('ABBcCAD', str.casefold) → A B c A D
        if key is None:
-           return map(operator.itemgetter(0), groupby(iterable))
-       return map(next, map(operator.itemgetter(1), groupby(iterable, key)))
+           return map(itemgetter(0), groupby(iterable))
+       return map(next, map(itemgetter(1), groupby(iterable, key)))
 
    def unique_everseen(iterable, key=None):
        "Yield unique elements, preserving order. Remember all elements ever seen."
@@ -941,13 +935,14 @@ and :term:`generators <generator>` which incur interpreter overhead.
    def unique(iterable, key=None, reverse=False):
       "Yield unique elements in sorted order. Supports unhashable inputs."
       # unique([[1, 2], [3, 4], [1, 2]]) → [1, 2] [3, 4]
-      return unique_justseen(sorted(iterable, key=key, reverse=reverse), key=key)
+      sequenced = sorted(iterable, key=key, reverse=reverse)
+      return unique_justseen(sequenced, key=key)
 
    def sliding_window(iterable, n):
        "Collect data into overlapping fixed-length chunks or blocks."
        # sliding_window('ABCDEFG', 4) → ABCD BCDE CDEF DEFG
        iterator = iter(iterable)
-       window = collections.deque(islice(iterator, n - 1), maxlen=n)
+       window = deque(islice(iterator, n - 1), maxlen=n)
        for x in iterator:
            window.append(x)
            yield tuple(window)
@@ -981,7 +976,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
        "Return all contiguous non-empty subslices of a sequence."
        # subslices('ABCD') → A AB ABC ABCD B BC BCD C CD D
        slices = starmap(slice, combinations(range(len(seq) + 1), 2))
-       return map(operator.getitem, repeat(seq), slices)
+       return map(getitem, repeat(seq), slices)
 
    def iter_index(iterable, value, start=0, stop=None):
        "Return indices where a value occurs in a sequence or iterable."
@@ -995,39 +990,40 @@ and :term:`generators <generator>` which incur interpreter overhead.
        else:
            stop = len(iterable) if stop is None else stop
            i = start
-           with contextlib.suppress(ValueError):
+           with suppress(ValueError):
                while True:
                    yield (i := seq_index(value, i, stop))
                    i += 1
 
-   def iter_except(func, exception, first=None):
+   def iter_except(function, exception, first=None):
        "Convert a call-until-exception interface to an iterator interface."
        # iter_except(d.popitem, KeyError) → non-blocking dictionary iterator
-       with contextlib.suppress(exception):
+       with suppress(exception):
            if first is not None:
                yield first()
            while True:
-               yield func()
+               yield function()
 
 
 The following recipes have a more mathematical flavor:
 
 .. testcode::
 
    def powerset(iterable):
+       "Subsequences of the iterable from shortest to longest."
        # powerset([1,2,3]) → () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)
        s = list(iterable)
        return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
 
    def sum_of_squares(iterable):
        "Add up the squares of the input values."
        # sum_of_squares([10, 20, 30]) → 1400
-       return math.sumprod(*tee(iterable))
+       return sumprod(*tee(iterable))
 
-   def reshape(matrix, cols):
+   def reshape(matrix, columns):
        "Reshape a 2-D matrix to have a given number of columns."
        # reshape([(0, 1), (2, 3), (4, 5)], 3) →  (0, 1, 2), (3, 4, 5)
-       return batched(chain.from_iterable(matrix), cols, strict=True)
+       return batched(chain.from_iterable(matrix), columns, strict=True)
 
    def transpose(matrix):
        "Swap the rows and columns of a 2-D matrix."
@@ -1038,7 +1034,7 @@ The following recipes have a more mathematical flavor:
        "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)
+       return batched(starmap(sumprod, product(m1, transpose(m2))), n)
 
    def convolve(signal, kernel):
        """Discrete linear convolution of two iterables.
@@ -1059,16 +1055,16 @@ The following recipes have a more mathematical flavor:
        n = len(kernel)
        padded_signal = chain(repeat(0, n-1), signal, repeat(0, n-1))
        windowed_signal = sliding_window(padded_signal, n)
-       return map(math.sumprod, repeat(kernel), windowed_signal)
+       return map(sumprod, repeat(kernel), windowed_signal)
 
    def polynomial_from_roots(roots):
        """Compute a polynomial's coefficients from its roots.
 
           (x - 5) (x + 4) (x - 3)  expands to:   x³ -4x² -17x + 60
        """
        # polynomial_from_roots([5, -4, 3]) → [1, -4, -17, 60]
-       factors = zip(repeat(1), map(operator.neg, roots))
-       return list(functools.reduce(convolve, factors, [1]))
+       factors = zip(repeat(1), map(neg, roots))
+       return list(reduce(convolve, factors, [1]))
 
    def polynomial_eval(coefficients, x):
        """Evaluate a polynomial at a specific value.
@@ -1081,7 +1077,7 @@ The following recipes have a more mathematical flavor:
        if not n:
            return type(x)(0)
        powers = map(pow, repeat(x), reversed(range(n)))
-       return math.sumprod(coefficients, powers)
+       return sumprod(coefficients, powers)
 
    def polynomial_derivative(coefficients):
        """Compute the first derivative of a polynomial.
@@ -1092,15 +1088,15 @@ The following recipes have a more mathematical flavor:
        # polynomial_derivative([1, -4, -17, 60]) → [3, -8, -17]
        n = len(coefficients)
        powers = reversed(range(1, n))
-       return list(map(operator.mul, coefficients, powers))
+       return list(map(mul, coefficients, powers))
 
    def sieve(n):
        "Primes less than n."
        # sieve(30) → 2 3 5 7 11 13 17 19 23 29
        if n > 2:
            yield 2
        data = bytearray((0, 1)) * (n // 2)
-       for p in iter_index(data, 1, start=3, stop=math.isqrt(n) + 1):
+       for p in iter_index(data, 1, start=3, stop=isqrt(n) + 1):
            data[p*p : n : p+p] = bytes(len(range(p*p, n, p+p)))
        yield from iter_index(data, 1, start=3)
 
@@ -1109,7 +1105,7 @@ The following recipes have a more mathematical flavor:
        # factor(99) → 3 3 11
        # factor(1_000_000_000_000_007) → 47 59 360620266859
        # factor(1_000_000_000_000_403) → 1000000000000403
-       for prime in sieve(math.isqrt(n) + 1):
+       for prime in sieve(isqrt(n) + 1):
            while not n % prime:
                yield prime
                n //= prime
@@ -1740,7 +1736,7 @@ The following recipes have a more mathematical flavor:
 
     # Old recipes and their tests which are guaranteed to continue to work.
 
-    def sumprod(vec1, vec2):
+    def old_sumprod_recipe(vec1, vec2):
         "Compute a sum of products."
         return sum(starmap(operator.mul, zip(vec1, vec2, strict=True)))
 
@@ -1823,7 +1819,7 @@ The following recipes have a more mathematical flavor:
     32
 
 
-    >>> sumprod([1,2,3], [4,5,6])
+    >>> old_sumprod_recipe([1,2,3], [4,5,6])
     32