[BangPypers] [Novice] Question on File seek and tell methods

saurabh saurabh.hirani at gmail.com
Mon Jun 17 14:58:57 CEST 2013

Well, if you must do it that way then this is what I cooked up in a hurry.
See if you like it. It comes with the caveat of recording the first
pattern's pos and re-reading the file from that pos again.

#!/usr/bin/env python

import re
import sys

# not doing input validation
# call program as: python prog.py start_keyword stop_keyword file_to_read
start_pattern = sys.argv[1]
stop_pattern = sys.argv[2]
inputfile = sys.argv[3]

re_start_pattern = re.compile(r'^%s$' % (start_pattern))
re_stop_pattern = re.compile(r'^%s$' % (stop_pattern))
pattern = re_start_pattern
last_line_len = 0

# this function should have a better name + check it for corner cases
def patternized_read(filename, pattern, printlines = False, start_at = 0):
    matched = False
    with open(inputfile) as f:
        f.seek(start_at, 0)
        pattern_pos = 0
        line = f.readline()
        while line:
            if printlines:
                print line
            match = re.search(pattern, line)
            # if the pattern matches
            if (match):
                matched = True
            pattern_pos = f.tell()
            line = f.readline()
    if matched:
        return pattern_pos
    return None

start_pos = patternized_read(inputfile, re_start_pattern)
if start_pos is None:
    print "start pattern %s is not present" % (start_pattern)
end_pos = patternized_read(inputfile, re_stop_pattern, printlines = True,
start_at = start_pos)

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