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Re: Strange behaviour with a for loop.

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  Re: Strange behaviour with a for loop. Chris Angelico <rosuav@gmail.com> - 2014-01-04 16:18 +1100

#63109 — Re: Strange behaviour with a for loop.

On Sat, Jan 4, 2014 at 3:03 PM, Sean Murphy <mhysnq1964@icloud.com> wrote:
>   filenames = sys.argv[1:]
>
> for filename in filenames:
>   print ("filename is: %s\n" %filename)

versus

>   filenames = sys.argv[1]
>
> for filename in filenames:
>   print ("filename is:  %s\n" % filename)

The first one is slicing sys.argv, so it returns another list. For
instance, sys.argv might be:

['foo.py', 'test', 'zxcv']

in which case sys.argv[1:] would be:

['test', 'zxcv']

which is still a list. But sys.argv[1] is a single string:

'test'

Now, when you use that in a for loop, you iterate over it. Iterating
over a list yields its items, as you'd expect. Iterating over a string
yields its characters. That's why you see it spelled out. Instead of
iterating over a list of file names, you're iterating over a single
file name, which isn't (in this case) all that useful.

Does that explain what you're seeing?

ChrisA

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