Question

I’ve built a script that takes a filename as an argument and extracts all lines that match a certain pattern. Trouble is I can’t open the filename – I keep getting :

"TypeError: coercing to unicode: need string or buffer"

It’s complaining about the line info = open(name, 'r').

Here’s the code:

import re
import sys
print sys.argv[1:]

keyword = 'queued='
pattern = re.compile(keyword)

name = sys.argv[1:]
inf = open(name, 'r') 
outf = open("test.txt", 'w')

for line in inf:
    if pattern.search(line):
        outf.write(line)

And I call it with

`extract.py trunc.log`

Any ideas what I’m doing wrong?

Answer 1

sys.argv[1:] is a list, not a string. When you slice a list, you get a list back — even if you only take 1 element with the slice. You need to give open a string. Perhaps you wanted sys.argv[-1] (the last element)?

As a side note, the python standard library provides commandline parsing options — One is the excellent argparse module which was introduced in python 2.7, but can be installed with very minimal effort on older python versions (I use it with python2.6 regularly).