Python: How to toggle between two values

Use itertools.cycle():

from itertools import cycle
myIterator = cycle(range(2))

myIterator.next()   # or next(myIterator) which works in Python 3.x. Yields 0
myIterator.next()   # or next(myIterator) which works in Python 3.x. Yields 1
# etc.

Note that if you need a more complicated cycle than [0, 1], this solution becomes MUCH more attractive than the other ones posted here...

from itertools import cycle
mySmallSquareIterator = cycle(i*i for i in range(10))
# Will yield 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 0, 1, 4, ...

You can accomplish that with a generator like this:

>>> def alternate():
...   while True:
...     yield 0
...     yield 1
...
>>>
>>> alternator = alternate()
>>>
>>> alternator.next()
0
>>> alternator.next()
1
>>> alternator.next()
0

you can use the mod (%) operator.

count = 0  # initialize count once

then

count = (count + 1) % 2

will toggle the value of count between 0 and 1 each time this statement is executed. The advantage of this approach is that you can cycle through a sequence of values (if needed) from 0 - (n-1) where n is the value you use with your % operator. And this technique does not depend on any Python specific features/libraries.

e.g.,

count = 0

for i in range(5):
     count = (count + 1) % 2
     print count

gives:

1
0
1
0
1