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Faster sieve() recipe (#98287)
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@ -809,15 +809,25 @@ which incur interpreter overhead.
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for k in range(len(roots) + 1)
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]
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def iter_index(seq, value, start=0):
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"Return indices where a value occurs in a sequence."
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# iter_index('AABCADEAF', 'A') --> 0 1 4 7
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i = start - 1
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try:
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while True:
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yield (i := seq.index(value, i+1))
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except ValueError:
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pass
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def sieve(n):
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"Primes less than n"
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# sieve(30) --> 2 3 5 7 11 13 17 19 23 29
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data = bytearray([1]) * n
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data[:2] = 0, 0
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limit = math.isqrt(n) + 1
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for p in compress(range(limit), data):
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data[p+p : n : p] = bytearray(len(range(p+p, n, p)))
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return compress(count(), data)
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"Primes less than n"
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# sieve(30) --> 2 3 5 7 11 13 17 19 23 29
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data = bytearray([1]) * n
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data[:2] = 0, 0
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limit = math.isqrt(n) + 1
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for p in compress(range(limit), data):
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data[p*p : n : p] = bytearray(len(range(p*p, n, p)))
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return iter_index(data, 1)
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def flatten(list_of_lists):
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"Flatten one level of nesting"
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@ -1170,6 +1180,15 @@ which incur interpreter overhead.
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>>> all(factored(x) == expanded(x) for x in range(-10, 11))
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True
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>>> list(iter_index('AABCADEAF', 'A'))
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[0, 1, 4, 7]
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>>> list(iter_index('AABCADEAF', 'B'))
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[2]
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>>> list(iter_index('AABCADEAF', 'X'))
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[]
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>>> list(iter_index('', 'X'))
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[]
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>>> list(sieve(30))
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[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
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>>> small_primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
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