Cycle over list indefinitely

python cycle through list
itertools
python cycle list
which construct can be used to iterate through a list
python yield
python continuously loop through list
enumerate through list python
import itertools
a = 1
b = 2
c = 3
x = a

def change_x():
    x = next??
    print("x:", x)

for i in range(10):
    change_x()

How can I cycle through a, b, c by calling change_x() indefinitely?

Output should be:

x: 2
x: 3
x: 1
x: 2
...

You could use cycle() and call next() as many times as you want to get cycled values.

from itertools import cycle

values = [1, 2, 3]
c = cycle(values)

for _ in range(10):
    print(next(c))

Output:

1
2
3
1
2
3
1
2
3
1

or as @chepner suggested without using next():

from itertools import islice

for i in islice(c, 10):
    print(i)

To get the same result.

Cycle over list indefinitely, You could use cycle() and call next() as many times as you want to get cycled values. from itertools import cycle values = [1, 2, 3] c = cycle(values) for _ in� In this article we will discuss different ways to iterate over a list. Iterate over the list using for-in loop. Its easies solution to iterate over the list i.e.

You can use itertools.cycle, to cycle around the values in a, b and c as specified:

from itertools import cycle
for i in cycle([a,b,c]):
    print(f'x: {i}')

Output

x: 1
x: 2
x: 0
x: 1
x: 2
x: 0
x: 1
x: 2
x: 0
x: 1
...

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this is what itertools.cycle does

import itertools,time

for i in itertools.cycle([1,2,3]):
    print(i)
    time.sleep(1)

The itertools Module: Infinite Iterators, These can be useful for generating numbers or cycling over iterables of unknown length, for example. In the code above, we create a simple list of polygons and pass them to cycle . Infinite iterators can be used to iterate indefinitely. The outer loop is not infinite, but the generator will continue to list its items indefinitely. – anonymous coward Oct 17 '12 at 23:25 Then go with Hans' response, however as an exercise, I would suggest you consider how to implement it yourself.

Just put your variables in a list then pick them this way:

mylist = [a,b,c]
i=0
while True:
   print(mylist[i%3])
   i+=1

Loop better: A deeper look at iteration in Python, There's no index initializing, bounds checking, or index incrementing. Python's for loops do all the work of looping over our numbers list for us. The one below will continue to cycle indefinitely, starting with an optional index: public static IEnumerable<T> Cycle<T> (this IEnumerable<T> list, int index = 0) { var count = list.Count(); index = index % count; while(true) { yield return list.ElementAt(index); index = (index + 1) % count; } }

If you want to define the function by hand then you use yield from:

def cycle(iterables):
    while True:
        yield from iterables

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Python Tutorial: Generators, Iterators are objects that can be iterated over like we do in a for loop. We can also say that an To do this, Python creates an iterator version of the list or string. In this case, an Then it repeats the sequence indefinitely. class Cycle(object):� Iteration means executing the same block of code over and over, potentially many times. A programming structure that implements iteration is called a loop. In programming, there are two types of iteration, indefinite and definite: With indefinite iteration, the number of times the loop is executed isn’t specified explicitly in advance. Rather

itertools – Iterator functions for efficient looping, Iterator-based code may be preferred over code which uses lists for several The count() function returns an interator that produces consecutive integers, indefinitely. The cycle() function returns an iterator that repeats the contents of the� The Air Force Life Cycle Management Center has awarded multiple indefinite-delivery / indefinite-quantity (IDIQ) contracts to The Boeing Co., General Atomics Aeronautical Systems Inc., Kratos Unmanned Aerial Systems, Inc. and Northrop Grumman Systems Corp. These initial awards will establish a

Comments
  • Are the variables a, b and c needed? Can you just cycle through a list? [1,2,3]
  • why does the output start from the value for b instead of a?
  • Most of the answer point you the right tool itertools.cycle but none actually answer your question. Define your change_x() function as the following: def change_x(c=cycle([a, b, c])): return next(c)
  • @Ashish: Yes the variables are needed they are acutely tk.StringVars in a GUI
  • @Sayse: It starts with b because print is after the first change
  • I like this solution because you take advantage of cycle as a generator and can get as few or many as you want
  • In fact, you don't even need to call next explicitly; for i in islice(c, 10): print(i).
  • to match OP's requirements (How can I cycle through a, b, c by calling change_x() indefinitely?) you can make it a function: def change_x(c=cycle([a, b, c])): return next(c)
  • @Yatu Having a infinite stream is useful for things like zipping with a sequence of finite but unknown length. It will give you "enough" in any case.
  • I was also thinking in the cases with multiple iterables, and some are finite. Wasn't so sure about a single iterable, but yes, that would indeed be one case where this could be useful. Thanks for pointing out @chepner