Why does list in program give an unexpected output?

Question

I am having a problem with my list in python.

I am printing out the list (working), a number that shows the line number (working) and an item in the list that should change every time the list is printed(not working?)

a = ["A", "B", "C", "D", "E"]
b = 0

for x in a:
    while b <= 10:

    print(a, x, b)
    b += 1

My current program output is

['A', 'B', 'C', 'D', 'E'] A 0
['A', 'B', 'C', 'D', 'E'] A 1
['A', 'B', 'C', 'D', 'E'] A 2
['A', 'B', 'C', 'D', 'E'] A 3

so on

the output I would like

['A', 'B', 'C', 'D', 'E'] A 0
['A', 'B', 'C', 'D', 'E'] B 1
['A', 'B', 'C', 'D', 'E'] C 2
['A', 'B', 'C', 'D', 'E'] D 3

and so on Although, when I try a different program it works perfectly?

list = ["a", "b", "c"]

for a in list:
    print(a)

Why does this happen and how can I fix it?

your for/while loop is not correctly indented. so it is hard to see what's wrong there. — hiro protagonist
– hiro protagonist, Commented Sep 15, 2015 at 7:14
I doubt your program outputs what you gave as "current program output". Even after fixing the indentation. — wap26
– wap26, Commented Sep 15, 2015 at 7:21
@Aymen first your code does not run as is (IndentationError) ; and if I indent either the print or the print and the b +=… in both cases the output is not what you mentioned. — wap26
– wap26, Commented Sep 15, 2015 at 7:28

Anand S Kumar · Accepted Answer · 2015-09-15 07:13:01Z

3

That is because you have the while loop inside the outer for loop (that iterates over the elements of the list. So the inner while loop only exists when b becomes greater than 10, and till then the value of x is A.

For what you want I would suggest using itertools.cycle(). Example -

>>> a = ["A", "B", "C", "D", "E"]
>>>
>>> b = 0
>>> import itertools
>>> acycle = itertools.cycle(a)
>>> for i in range(11):
...     print(a,next(acycle),i)
...
['A', 'B', 'C', 'D', 'E'] A 0
['A', 'B', 'C', 'D', 'E'] B 1
['A', 'B', 'C', 'D', 'E'] C 2
['A', 'B', 'C', 'D', 'E'] D 3
['A', 'B', 'C', 'D', 'E'] E 4
['A', 'B', 'C', 'D', 'E'] A 5
['A', 'B', 'C', 'D', 'E'] B 6
['A', 'B', 'C', 'D', 'E'] C 7
['A', 'B', 'C', 'D', 'E'] D 8
['A', 'B', 'C', 'D', 'E'] E 9
['A', 'B', 'C', 'D', 'E'] A 10

answered Sep 15, 2015 at 7:13

Anand S Kumar

91.5k18 gold badges196 silver badges179 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

pzelasko · Accepted Answer · 2015-09-15 07:14:24Z

2

You have a double loop here (while inside for) and you never reset the b to 0. To get the result you expected, you should use enumerate:

for idx, x in enumerate(a):
    print(a, x, idx)

answered Sep 15, 2015 at 7:14

pzelasko

2,4223 gold badges18 silver badges24 bronze badges

Collectives™ on Stack Overflow

Why does list in program give an unexpected output?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related