How do I re.search or re.match on a whole file without reading it all into memory?

file, performance, python, regex

Solution

You can use mmap to map the file to memory. The file contents can then be accessed like a normal string:

import re, mmap

with open('/var/log/error.log', 'r+') as f:
  data = mmap.mmap(f.fileno(), 0)
  mo = re.search('error: (.*)', data)
  if mo:
    print "found error", mo.group(1)

This also works for big files, the file content is internally loaded from disk as needed.

Problem

I want to be able to run a regular expression on an entire file, but I'd like to be able to not have to read the whole file into memory at once as I may be working with rather large files in the future. Is there a way to do this? Thanks! Clarification: I cannot read line-by-line because it can span multiple lines.

Original source