Loop through a list using a while statement

Question

I want to loop through a list and terminate when I reach a certain value. Something like:

ls = ['yes','yes','stop','yes']

while a in ls <> 'stop':
    print a

Would print:

yes
yes

I know I can do:

for a in ls:
    if a == 'stop':
        break
    print a

but it seems messy.

It might be "messy", but it is perfectly clear & does the job — Scott Hunter
– Scott Hunter, Commented Dec 18, 2014 at 2:50
Also, you should not be using <>. That operator was deprecated in Python 2.5 and removed entirely from Python 3.x. You should be using != instead. — user2555451
– user2555451, Commented Dec 18, 2014 at 3:01

tckmn · Accepted Answer · 2014-12-18 02:47:13Z

4

You could use list indexing and slicing:

print ls[:ls.index('stop')]
# => ['yes', 'yes']

In a loop:

for a in ls[:ls.index('stop')]:
    print a

answered Dec 18, 2014 at 2:47

tckmn

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user2555451 · Accepted Answer · 2014-12-18 02:48:51Z

4

You could use itertools.takewhile:

>>> from itertools import takewhile
>>> ls = ['yes','yes','stop','yes']
>>> for i in takewhile(lambda x: x != 'stop', ls):
...     i
...
'yes'
'yes'
>>>

answered Dec 18, 2014 at 2:48

user2555451

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