passing variable to loop as string in python

Question

I have a python script that will take each file in a directory, iterate through the contents of the file and create an output file for each input file. This output file may have duplicate entries and if it does I would like to take only the unique values similar to the UNIX command

uniq -u input.file > output.file

Although I could use shell scripts to do this I would like to include a line of python that will take only unique values. I know i can do this:

import os
os.system("uniq -u input.file > output.file")

However when I attempt to put this in a loop so that it will make unique all of the files I just made:

for curfile in fs:
    if curfile[-3:]=='out':
        os.system("uniq -u %s > %s") % (str(curfile), str(curfile[:-4] + ".uniq")

I get the following error:

unsupported operand type(s) for %: 'int' and 'tuple'

I have tried a few syntaxes to try to get the variables recognized but can't find a similar enough example on the web. Any suggestions would be greatly appreciated.

You've forgotten a ) in os.system("uniq -u %s > %s") % (str(curfile), str(curfile[:-4] + ".uniq"). — Griffin
– Griffin, Commented Oct 29, 2011 at 18:37
the parenthesis for os.system should encolose all of the rest of line, shouldnt it? — yosukesabai
– yosukesabai, Commented Oct 29, 2011 at 18:38
It's not just a missing paren -- you've also got one in the wrong place. — agf
– agf, Commented Oct 29, 2011 at 18:43
Note that ideally, you should be using subprocess.call() instead of os.system(). — Amber
– Amber, Commented Oct 29, 2011 at 18:44

agf · Accepted Answer · 2011-10-29 18:38:37Z

3

You have

os.system(
             "uniq -u %s > %s"
         ) % ( # The % and this paren should be inside the call to os.system
                 str(curfile), 
                 str(curfile[:-4] + ".uniq")
               # you're missing a close paren here

you need

os.system(
             "uniq -u %s > %s" % (
                                     str(curfile), 
                                     str(curfile[:-4] + ".uniq")
                                 )
         )

First you format the string, then it goes to os.system -- as you have it now, the string goes to os.system then you attempt to % the result, which is an int. (The return code of uniq.)

answered Oct 29, 2011 at 18:38

agf

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