[Chicago] islice on Nested Iterators

[Oren Livne]

Dear All,

I'm trying to reuse the solution at the end of 
http://stackoverflow.com/questions/470690/how-to-automatically-generate-n-distinct-colors 
for Python 2.7. Unfortunately, the code below never returns, since even 
though islice() requests the first 100 iterates, it seems that the 
inner-map calls like

gethsvs = lambda: flatten(itertools.imap(genhsv, getfracs()))

force getting all iterates. Instead of passing the number of iterates to 
all lambda functions, is there a way to make an islice() call at the 
main code, as below, but making it get only the first 100 iterates in 
all inner maps as well?

Thanks,
Oren

---------------------

import colorsys, itertools, numpy as np
from fractions import Fraction

def zenos_dichotomy():
     '''
http://en.wikipedia.org/wiki/1/2_%2B_1/4_%2B_1/8_%2B_1/16_%2B_%C2%B7_%C2%B7_%C2%B7
     '''
     for k in itertools.count():
         yield Fraction(1, 2 ** k)

def getfracs():
     '''
     [Fraction(0, 1), Fraction(1, 2), Fraction(1, 4), Fraction(3, 4), 
Fraction(1, 8), Fraction(3, 8), Fraction(5, 8), Fraction(7, 8), 
Fraction(1, 16), Fraction(3, 16), ...]
     [0.0, 0.5, 0.25, 0.75, 0.125, 0.375, 0.625, 0.875, 0.0625, 0.1875, ...]
     '''
     yield 0
     for k in zenos_dichotomy():
         i = k.denominator # [1,2,4,8,16,...]
         for j in range(1, i, 2):
             yield Fraction(j, i)

'''Can be used for the v in hsv to map linear values 0..1 to something 
that looks equidistant.'''
bias = lambda x: (np.sqrt(x / 3) / Fraction(2, 3) + Fraction(1, 3)) / 
Fraction(6, 5)

def genhsv(h):
     for s in [Fraction(6, 10)]: # optionally use range
         for v in [Fraction(8, 10), Fraction(5, 10)]: # could use range too
             yield (h, s, v) # use bias for v here if you use range

genrgb = lambda x: colorsys.hsv_to_rgb(*x)
flatten = itertools.chain.from_iterable
gethsvs = lambda: flatten(itertools.imap(genhsv, getfracs()))
getrgbs = lambda: itertools.imap(genrgb, gethsvs())

def genhtml(x):
     uint8tuple = itertools.imap(lambda y: int(y * 255), x)
     return 'rgb({},{},{})'.format(*uint8tuple)

gethtmlcolors = lambda: map(genhtml, getrgbs())

if __name__ == '__main__':
     print(list(itertools.islice(gethtmlcolors(), 100)))

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