def line_number(filename, string_to_match):
    """Helper function to return the line number of the first matched string."""
    with open(filename, 'r') as f:
        for i, line in enumerate(f):
            if line.find(string_to_match) != -1:
                # Found our match.
                return i+1
    raise Exception("Unable to find '%s' within file %s" % (string_to_match, filename))