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[3.11] Add recipes to showcase tee(), zip*, batched, starmap, and product. #101028

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Merged
merged 3 commits into from
Jan 14, 2023
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[3.11] Add recipes to showcase tee(), zip*, batched, starmap, and product. #101028

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b1b0508
Add recipes to showcase tee(), zip*, batched, starmap, and product.
rhettinger Jan 14, 2023
c4483ae
Move batched() recipe before its first use.
rhettinger Jan 14, 2023
1a6b62b
Keep grouper() in proximity with batched().
rhettinger Jan 14, 2023
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75 changes: 51 additions & 24 deletions Doc/library/itertools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -799,10 +799,50 @@ which incur interpreter overhead.
"Returns the sequence elements n times"
return chain.from_iterable(repeat(tuple(iterable), n))

def batched(iterable, n):
"Batch data into tuples of length n. The last batch may be shorter."
# batched('ABCDEFG', 3) --> ABC DEF G
if n < 1:
raise ValueError('n must be at least one')
it = iter(iterable)
while (batch := tuple(islice(it, n))):
yield batch

def grouper(iterable, n, *, incomplete='fill', fillvalue=None):
"Collect data into non-overlapping fixed-length chunks or blocks"
# grouper('ABCDEFG', 3, fillvalue='x') --> ABC DEF Gxx
# grouper('ABCDEFG', 3, incomplete='strict') --> ABC DEF ValueError
# grouper('ABCDEFG', 3, incomplete='ignore') --> ABC DEF
args = [iter(iterable)] * n
if incomplete == 'fill':
return zip_longest(*args, fillvalue=fillvalue)
if incomplete == 'strict':
return zip(*args, strict=True)
if incomplete == 'ignore':
return zip(*args)
else:
raise ValueError('Expected fill, strict, or ignore')

def sumprod(vec1, vec2):
"Compute a sum of products."
return sum(starmap(operator.mul, zip(vec1, vec2, strict=True)))

def sum_of_squares(it):
"Add up the squares of the input values."
# sum_of_squares([10, 20, 30]) -> 1400
return 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(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)
Expand Down Expand Up @@ -886,30 +926,6 @@ which incur interpreter overhead.
return starmap(func, repeat(args))
return starmap(func, repeat(args, times))

def grouper(iterable, n, *, incomplete='fill', fillvalue=None):
"Collect data into non-overlapping fixed-length chunks or blocks"
# grouper('ABCDEFG', 3, fillvalue='x') --> ABC DEF Gxx
# grouper('ABCDEFG', 3, incomplete='strict') --> ABC DEF ValueError
# grouper('ABCDEFG', 3, incomplete='ignore') --> ABC DEF
args = [iter(iterable)] * n
if incomplete == 'fill':
return zip_longest(*args, fillvalue=fillvalue)
if incomplete == 'strict':
return zip(*args, strict=True)
if incomplete == 'ignore':
return zip(*args)
else:
raise ValueError('Expected fill, strict, or ignore')

def batched(iterable, n):
"Batch data into tuples of length n. The last batch may be shorter."
# batched('ABCDEFG', 3) --> ABC DEF G
if n < 1:
raise ValueError('n must be at least one')
it = iter(iterable)
while (batch := tuple(islice(it, n))):
yield batch

def triplewise(iterable):
"Return overlapping triplets from an iterable"
# triplewise('ABCDEFG') --> ABC BCD CDE DEF EFG
Expand Down Expand Up @@ -1184,6 +1200,17 @@ which incur interpreter overhead.
>>> sumprod([1,2,3], [4,5,6])
32

>>> 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]
Expand Down