What is the python equivalent of grep -v?

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])