What is the python equivalent of grep -v?

Question

I like grep -v. I use it all the time. But I am also doing some text processing in python, and there is one crucial thing that I lack.

Usually, I use grep -v to take extraneous stuff out of text.

For instance,

$grep -v [a-z]
(confirms that I don't want those lines)
$grep [a-z] > linesiwanted

But how do I match the complement of a regex in Python? For instance, the complement of \w?

Answer 1

A regex in Python, either the search or match methods, returns a Match object or None. For grep -v equivalent, you might use:

import re
for line in sys.stdin:
    if re.search(r'[a-z]', line) is None:
        sys.stdout.write(line)

Or more concisely:

import re; sys.stdout.writelines([line for line in sys.stdin if re.search(r'[a-z]', line) is None])

Answer 2

It turns out you can just use [^a-z] to mean grep -v [a-z].

I'm using it like:

#!/usr/bin/env python
# coding=UTF-8

import sys, re

for file in sys.argv[1:]:
    f = open(file)
    string = f.read()
    regex = re.compile('[^a-z]')
    subs = regex.sub('', string)
    f.close()
    print subs