How to implement this python generator

Question

I try to create a generator in python who returns this :

itemList = []
for i in myGenerator(12):
    itemList.append(i)
print itemList
>>> [0 0.334, 1, 2, 3, 4, 5, 6, 7, 8, 8.667, 9]

This is what I have at the moment :

def myGenerator(index) :
    indexList = xrange(index)
    for i in indexList :
        if i == 0:
            yield 0
        elif i == 1:
            yield i/3.0
        elif i == indexList[-2]:
            yield indexList[-3] - (1 / 3.0)
        elif i == indexList[-1]:
             yield i-2
        else :
            yield i-1

for i in myGenerator(12):
    print(i)

But it seems not clean ... Is there another way around?

You can't pass a generator to the xrange function; not sure what you wanted to achieve with that? — Martijn Pieters
– Martijn Pieters, Commented Aug 22, 2012 at 9:29
That was a mistake .. It's for a script who generate the position of NURBS CVs in Maya. — MObject
– MObject, Commented Aug 22, 2012 at 9:33
what exactly are you trying to do ? it seems like a very odd list to generate — Inbar Rose
– Inbar Rose, Commented Aug 22, 2012 at 9:37
python wise, this seems ok, if you can write your algorithm in a more efficient way, i don't know, since I don't understand it. — schacki
– schacki, Commented Aug 22, 2012 at 9:40

ecatmur · Accepted Answer · 2012-08-22 09:39:05Z

3

I'd construct the range piecewise:

from itertools import chain
def myGenerator(index):
    return chain([0, 1 / 3.0], xrange(1, index - 3), [index - 3 - 1 / 3.0, index - 3])

list(myGenerator(12))
[0, 0.33333333333333331, 1, 2, 3, 4, 5, 6, 7, 8, 8.6666666666666661, 9]

answered Aug 22, 2012 at 9:39

ecatmur

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Comments

MatthieuW · Accepted Answer · 2012-08-22 12:42:39Z

3

If you want to stay close to your original idea but without the "if...elif...else" structure:

def myGenerator(index) :
    yield 0
    yield 1/3.0
    for i in xrange(1, index-3):
        yield i
    yield index - 3 - 1/3.0
    yield index - 3

answered Aug 22, 2012 at 12:42

MatthieuW

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