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From: Peter Otten <__peter__@web.de>
Subject: Re: Any algorithm to preserve whitespaces?
Date: Wed, 23 Jan 2013 23:04:02 +0100
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Xref: csiph.com comp.lang.python:37510

Santosh Kumar wrote:

> Yes, Peter got it right.
> 
> Now, how can I replace:
> 
>     script, givenfile = argv
> 
> with something better that takes argv[1] as input file as well as
> reads input from stdin.
> 
> By input from stdin, I mean that currently when I do `cat foo.txt |
> capitalizr` it throws a ValueError error:
> 
>     Traceback (most recent call last):
>       File "/home/santosh/bin/capitalizr", line 16, in <module>
>         script, givenfile = argv
>     ValueError: need more than 1 value to unpack
> 
> I want both input methods.

You can use argparse and its FileType:

import argparse
import sys

parser = argparse.ArgumentParser()
parser.add_argument("infile", type=argparse.FileType("r"), nargs="?", 
default=sys.stdin)
args = parser.parse_args()

for line in args.infile:
    print line.strip().title() # replace with your code


As this has the small disadvantage that infile is opened immediately I tend 
to use a slight variation:

import argparse
import sys
from contextlib import contextmanager

@contextmanager
def xopen(filename):
    if filename is None or filename == "-":
        yield sys.stdin
    else:
        with open(filename) as instream:
            yield instream

parser = argparse.ArgumentParser()
parser.add_argument("infile", nargs="?")
args = parser.parse_args()

with xopen(args.infile) as instream:
    for line in instream:
        print line.strip().title()