New submission from David W. Lambert <b49p23t...@stny.rr.com>:
Raymond Hettinger posted clever Hamming number generator,
http://code.activestate.com/recipes/576961/
which I tried to modify. The function gives incorrect output when
called as hamming_numbers(shorthand = True). It seemed reasonable to
expect the two arrangements of statements controlled by the shorthand
boolean to be functionally equivalent.
http://docs.python.org/3.1/reference/executionmodel.html is relevant,
and makes me think this is not a bug, but I wish it were. I'd
appreciate your determination. Thanks, Dave.
from itertools import tee, chain, islice, groupby
from heapq import merge
def hamming_numbers(shorthand = False):
def deferred_output():
for i in output:
yield i
result, p2, p3, p5 = tee(deferred_output(), 4)
if shorthand: # Lambert modification
m = [(a*x for x in p) for (a,p,) in ((2,p2),(3,p3),(5,p5))]
assert m[0] is not m[2]
merged = merge(*m)
else: # original
m2 = (2*x for x in p2)
m3 = (3*x for x in p3)
m5 = (5*x for x in p5)
merged = merge(m2, m3, m5)
combined = chain([1], merged)
output = (k for k, v in groupby(combined))
return result
if __name__ == '__main__':
print(list(islice(hamming_numbers(), 10)))
print(list(islice(hamming_numbers(True), 10)))
----------
components: Interpreter Core
messages: 95981
nosy: LambertDW
severity: normal
status: open
title: Bug or expected behavior? I cannot tell.
type: behavior
versions: Python 3.1
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue7439>
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