how to iterate using itertools for iterables having different lengths in python?

Question

I have two iterables of different length as follows

  range(5)
  numpy.arange(0,0.3,0.1)

I want to have pairs as follows

    (0,0.)
    (1,0.)
    (2,0.)
    (3,0.)
    (4,0.)

    (0,0.1)
    (1,0.1)
    (2,0.1)
    (3,0.1)
    (4,0.1)

    (0,0.2)
    (1,0.2)
    (2,0.2)
    (3,0.2)
    (4,0.2)

How one could do it using itertools?

Answer 1

Generally a job for itertools.product:

>>> from itertools import product
>>> for x in product(range(5), numpy.arange(0, 0.3, 0.1)):
    print x
...     
(0, 0.0)
(0, 0.10000000000000001)
(0, 0.20000000000000001)
(1, 0.0)
(1, 0.10000000000000001)
(1, 0.20000000000000001)
(2, 0.0)
(2, 0.10000000000000001)
(2, 0.20000000000000001)
(3, 0.0)
(3, 0.10000000000000001)
(3, 0.20000000000000001)
(4, 0.0)
(4, 0.10000000000000001)
(4, 0.20000000000000001)

Since you want the 'other' order, you could use a comprehension:

>>> [(x,y) for y in numpy.arange(0, 0.3, 0.1) for x in range(5)]

[(0, 0.0),
 (1, 0.0),
 (2, 0.0),
 (3, 0.0),
 (4, 0.0),
 (0, 0.10000000000000001),
 (1, 0.10000000000000001),
 (2, 0.10000000000000001),
 (3, 0.10000000000000001),
 (4, 0.10000000000000001),
 (0, 0.20000000000000001),
 (1, 0.20000000000000001),
 (2, 0.20000000000000001),
 (3, 0.20000000000000001),
 (4, 0.20000000000000001)]

Or you could reverse the arguments and then reverse each tuple that itertools.product spits out (they always cycle the rightmost element the quickest).

>>> [x[::-1] for x in product(numpy.arange(0, 0.3, 0.1), range(5))]

[(0, 0.0),
 (1, 0.0),
 (2, 0.0),
 (3, 0.0),
 (4, 0.0),
 (0, 0.10000000000000001),
 (1, 0.10000000000000001),
 (2, 0.10000000000000001),
 (3, 0.10000000000000001),
 (4, 0.10000000000000001),
 (0, 0.20000000000000001),
 (1, 0.20000000000000001),
 (2, 0.20000000000000001),
 (3, 0.20000000000000001),
 (4, 0.20000000000000001)]