Python: How can you iterate over a list that is nested inside a while-loop?

Question

I have the following code:

shape = input("Please enter your choice of shape? ")    

nthTime = ["second","third","fourth","fifth","sixth"]

while shape.lower() not in ["octagon","heptagon","hexagon"] :
    print("Please select a shape from the list!")
    shape = input("Pick a shape, for the " + nthTime + " time! ")

How can I achieve the outcome, that Python will iterate over the list 'nthTime', each time it passes through the `while-loop?

I could use a nested for-loop but of course this would run the whole list, which is not my aim.

Therefore, I conclude that I would need to use a nested while-loop; however I cannot figure out the exact syntax.

I'm hoping this will be a useful question for others also in the future.

A nested for loop under the while over `nthTime` **will** *iterate over the list each time it passes through the while-loop*. What is your problem? — OneCricketeer, Jan 02 '16 at 18:15
may i guess you want something like `shape = input("Pick a shape, for the " + nthTime[iteration_index] + " time! ")`? — Netwave, Jan 02 '16 at 18:16

score 2 · Answer 1 · answered Jan 02 '16 at 18:19

2

Use a for-loop and break out of the loop only if the user enters the correct value

for iteration in nthTime:
    if shape.lower() not in ["octagon","heptagon","hexagon"]:
        print("Please select a shape from the list!")
        shape = input("Pick a shape, for the " + iteration + " time! ")
    else: break
else: print "You have wasted all your chances, try again later"

answered Jan 02 '16 at 18:19

smac89

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Thank you. Is it at all possible to iterate over a list using a while-loop? – Andrew Hardiman Jan 02 '16 at 18:51

Iron Fist · Accepted Answer · 2016-01-02T18:24:22.587

Something like this:

shape = input("Please enter your choice of shape? ")    

nthTime = ["second","third","fourth","fifth","sixth"]
undesired_shapes = ["octagon","heptagon","hexagon"]

indx = 0

while shape.lower() not in undesired_shapes:
    print("Please select a shape from the list!")
    shape = input("Pick a shape, for the " + nthTime[indx] + " time! ")
    indx += 1
    if indx >= len(nthTime):
        print 'Giving up !!'
        break

donopj2 · Answer 3 · 2016-01-02T18:29:37.620

0

nthTime.reverse()

while shape.lower() not in ["octagon","heptagon","hexagon"] and nthTime:
    print("Please select a shape from the list!")
    shape = input("Pick a shape, for the " + nthTime.pop() + " time! ")

edited Jan 02 '16 at 18:29

answered Jan 02 '16 at 18:16

donopj2

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You don't need to reverse the list and essentially make it a stack... – OneCricketeer Jan 02 '16 at 18:17
No need to reverse. You can simply do `nthTime.pop(0)` – Ahsanul Haque Jan 02 '16 at 18:54
Or he could just define the string literals in the right order. It's a trivial question, I reversed to minimize the changes to the code. I was showing him how to use a stack to exhaust the attempts. – donopj2 Jan 02 '16 at 18:56

Python: How can you iterate over a list that is nested inside a while-loop?

3 Answers3