[feature-request] addition of cyclers requires them to be equal length

[bjmuld]

I often need to combine cyclers of unequal length. I had been under the impression that the salient feature distinguishing the '*' and '+' operations was whether or not the cyclers being joined were of equal length, but after submitting matplotlib/cycler #50, it seems that '*' is intended to combine them in a hierarchical fashion, where '+' yields simultaneous cycling.

Currently, '+' does not support unequal-length cyclers, leaving the user to solve the problem of finding the LCM of the two cyclers and extending their length appropriately. Though not insurmountable, it's a significant distraction from other work.

Thoughts?

from matplotlib.pyplot import cycler

prop_orders = {
    'color': ['k', 'r', 'g', 'b', 'c', 'm', 'y'],
    'marker': ['.', 'o', 'v', 's', '*'],
}

a=cycler('color', prop_orders['color'])
b=cycler('marker', prop_orders['marker'])

c = (a*b)()

print(next(c))
print(next(c))

Actual outcome

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "", line 242, in __add__
    "not {0} and {1}".format(len(self), len(other)))
ValueError: Can only add equal length cycles, not 7 and 5

Desired outcome
I would hope for the operation to succeed and for both attributes to be actively cycling, i.e.

{'color': 'k', 'marker': '.'}
{'color': 'r', 'marker': 'o'}

[bjmuld]

duplicate :/