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Strange behaviour with a for loop.

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  Strange behaviour with a for loop. Sean Murphy <mhysnq1964@icloud.com> - 2014-01-04 15:03 +1100
    Re: Strange behaviour with a for loop. Larry Hudson <orgnut@yahoo.com> - 2014-01-04 13:25 -0800

#63107 — Strange behaviour with a for loop.

Hello all.

This is a newly question. But I wish to understand why the below code is providing different results.

import os, sys


if len(sys.argv) > 2:
  filenames = sys.argv[1:]
else
  print ("no parameters provided\n")
  sys.edit()

for filename in filenames:
  print ("filename is: %s\n" %filename)

The above code will return results like:

filename is test.txt

If I modify the above script slightly as shown below, I get a completely different result. 

if len(sys.argv) > 2:
  filenames = sys.argv[1]
else
  print ("no parameters provided\n")
  sys.exit()

for filename in filenames:
  print ("filename is:  %s\n" % filename)

The result is the filename is spelled out a character at a time. The bit I am missing is something to do with splicing or referencing in Python.

Why am I getting different results? In other languages I would have got the whole content of the element when using the index of the array (list).


Sean 
filename is: t
filename 

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#63144

On 01/03/2014 08:03 PM, Sean Murphy wrote:
> Hello all.
>
> This is a newly question. But I wish to understand why the below code is providing different results.
>
> import os, sys
>
>
> if len(sys.argv) > 2:
>    filenames = sys.argv[1:]
> else
>    print ("no parameters provided\n")
>    sys.edit()
>
> for filename in filenames:
>    print ("filename is: %s\n" %filename)
>
> The above code will return results like:
>
> filename is test.txt
>
> If I modify the above script slightly as shown below, I get a completely different result.
>
> if len(sys.argv) > 2:
>    filenames = sys.argv[1]
> else
>    print ("no parameters provided\n")
>    sys.exit()
>
> for filename in filenames:
>    print ("filename is:  %s\n" % filename)
>
> The result is the filename is spelled out a character at a time. The bit I am missing is something to do with splicing or referencing in Python.
>
> Why am I getting different results? In other languages I would have got the whole content of the element when using the index of the array (list).
>
>
> Sean
> filename is: t
> filename
>

How easy it is to overlook your own typos...  (No worry, everybody does it)   ;-)

In your first version you have:  filenames = sys.argv[1:]
which gives you a list of filenames (which is what you want).

In your second version you have:  filenames = sys.argv[1]
which is ONE item -- a string, not a list.  You left out the colon.

      -=- Larry -=-

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