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Better presentation order for recipes. (gh-116755)
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@ -785,8 +785,8 @@ well as with the built-in itertools such as ``map()``, ``filter()``,
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A secondary purpose of the recipes is to serve as an incubator. The
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``accumulate()``, ``compress()``, and ``pairwise()`` itertools started out as
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recipes. Currently, the ``sliding_window()`` and ``iter_index()`` recipes
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are being tested to see whether they prove their worth.
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recipes. Currently, the ``sliding_window()``, ``iter_index()``, and ``sieve()``
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recipes are being tested to see whether they prove their worth.
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Substantially all of these recipes and many, many others can be installed from
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the `more-itertools project <https://pypi.org/project/more-itertools/>`_ found
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@ -795,12 +795,12 @@ on the Python Package Index::
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python -m pip install more-itertools
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Many of the recipes offer the same high performance as the underlying toolset.
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Superior memory performance is kept by processing elements one at a time
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rather than bringing the whole iterable into memory all at once. Code volume is
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kept small by linking the tools together in a functional style which helps
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eliminate temporary variables. High speed is retained by preferring
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"vectorized" building blocks over the use of for-loops and :term:`generator`\s
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which incur interpreter overhead.
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Superior memory performance is kept by processing elements one at a time rather
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than bringing the whole iterable into memory all at once. Code volume is kept
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small by linking the tools together in a `functional style
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<https://www.cs.kent.ac.uk/people/staff/dat/miranda/whyfp90.pdf>`_. High speed
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is retained by preferring "vectorized" building blocks over the use of for-loops
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and :term:`generators <generator>` which incur interpreter overhead.
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.. testcode::
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@ -873,6 +873,14 @@ which incur interpreter overhead.
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"Returns True if all the elements are equal to each other."
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return len(take(2, groupby(iterable, key))) <= 1
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def unique_justseen(iterable, key=None):
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"List unique elements, preserving order. Remember only the element just seen."
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# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
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# unique_justseen('ABBcCAD', str.casefold) --> A B c A D
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if key is None:
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return map(operator.itemgetter(0), groupby(iterable))
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return map(next, map(operator.itemgetter(1), groupby(iterable, key)))
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def unique_everseen(iterable, key=None):
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"List unique elements, preserving order. Remember all elements ever seen."
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# unique_everseen('AAAABBBCCDAABBB') --> A B C D
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@ -889,35 +897,6 @@ which incur interpreter overhead.
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seen.add(k)
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yield element
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def unique_justseen(iterable, key=None):
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"List unique elements, preserving order. Remember only the element just seen."
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# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
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# unique_justseen('ABBcCAD', str.casefold) --> A B c A D
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if key is None:
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return map(operator.itemgetter(0), groupby(iterable))
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return map(next, map(operator.itemgetter(1), groupby(iterable, key)))
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def iter_index(iterable, value, start=0, stop=None):
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"Return indices where a value occurs in a sequence or iterable."
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# iter_index('AABCADEAF', 'A') --> 0 1 4 7
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seq_index = getattr(iterable, 'index', None)
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if seq_index is None:
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# Path for general iterables
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it = islice(iterable, start, stop)
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for i, element in enumerate(it, start):
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if element is value or element == value:
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yield i
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else:
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# Path for sequences with an index() method
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stop = len(iterable) if stop is None else stop
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i = start
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try:
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while True:
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yield (i := seq_index(value, i, stop))
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i += 1
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except ValueError:
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pass
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def sliding_window(iterable, n):
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"Collect data into overlapping fixed-length chunks or blocks."
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# sliding_window('ABCDEFG', 4) --> ABCD BCDE CDEF DEFG
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@ -967,6 +946,27 @@ which incur interpreter overhead.
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slices = starmap(slice, combinations(range(len(seq) + 1), 2))
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return map(operator.getitem, repeat(seq), slices)
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def iter_index(iterable, value, start=0, stop=None):
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"Return indices where a value occurs in a sequence or iterable."
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# iter_index('AABCADEAF', 'A') --> 0 1 4 7
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seq_index = getattr(iterable, 'index', None)
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if seq_index is None:
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# Path for general iterables
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it = islice(iterable, start, stop)
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for i, element in enumerate(it, start):
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if element is value or element == value:
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yield i
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else:
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# Path for sequences with an index() method
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stop = len(iterable) if stop is None else stop
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i = start
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try:
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while True:
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yield (i := seq_index(value, i, stop))
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i += 1
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except ValueError:
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pass
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def iter_except(func, exception, first=None):
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""" Call a function repeatedly until an exception is raised.
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@ -1047,8 +1047,8 @@ The following recipes have a more mathematical flavor:
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Computes with better numeric stability than Horner's method.
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"""
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# Evaluate x³ -4x² -17x + 60 at x = 2.5
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# polynomial_eval([1, -4, -17, 60], x=2.5) --> 8.125
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# Evaluate x³ -4x² -17x + 60 at x = 5
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# polynomial_eval([1, -4, -17, 60], x=5) --> 0
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n = len(coefficients)
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if not n:
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return type(x)(0)
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@ -1311,10 +1311,10 @@ The following recipes have a more mathematical flavor:
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>>> from fractions import Fraction
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>>> from decimal import Decimal
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>>> polynomial_eval([1, -4, -17, 60], x=2)
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18
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>>> x = 2; x**3 - 4*x**2 -17*x + 60
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18
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>>> polynomial_eval([1, -4, -17, 60], x=5)
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0
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>>> x = 5; x**3 - 4*x**2 -17*x + 60
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0
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>>> polynomial_eval([1, -4, -17, 60], x=2.5)
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8.125
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>>> x = 2.5; x**3 - 4*x**2 -17*x + 60
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