asx.py

import os

def get_block_range (filename, lookupValue):
    """
    Returns the index of the first line that contain ``lookupValue``
    and end of the file
    # here the value was at line 941 and the file had 1000 lines.

    >>> get_block_range('example.txt', 'example')
    (941, 1000)

    :rtype: tuple
    """
    if not os.path.getsize(filename):
        return None, 0

    with open(filename, 'r') as file:
        lookup_position = None

        for num, line in enumerate(file, 1):
            if lookup_position is None and lookupValue in line:
                lookup_position = num
        return lookup_position, num

example.txt

asx
asx
as
x
asxfsdvsf
gbs
bs
dfv
sdfvsdf
bsb
dfv
example


gsf
b
fg
bsf
gb
sfgb
sfg
b
sfgb
sf
bg
sfg
b

traceback

In [10]: asx.get_block_range('example.txt', 'example')
Out[10]: (12, 27)