Back and forth loop Python

Question

I want to create an infinite loop that counts up and down from 0 to 100 to 0 (and so on) and only stops when some convergence criterion inside the loop is met, so basically something like this:

for i in range(0, infinity):     for j in range(0, 100, 1):         print(j) # (in my case 100 lines of code)     for j in range(100, 0, -1):         print(j) # (same 100 lines of code as above) 

Is there any way to merge the two for loops over j into one so that I don't have write out the same code inside the loops twice?

Answer 1

Use the chain method of itertools

import itertools for i in range(0, infinity):     for j in itertools.chain(range(0, 100, 1), range(100, 0, -1)):         print(j) # (in my case 100 lines of code) 

As suggested by @Chepner, you can use itertools.cycle() for the infinite loop:

from itertools import cycle, chain  for i in cycle(chain(range(0, 100, 1), range(100, 0, -1))):     ....