Searching through text files for text pattern match

__author__ = 'Work'
'''
You want to keep a limited history of the last few items seen during iteration or during some other kind of processing.

Keeping a limited history is a perfect use for a collections.deque. For example, the following code performs a simple text match
on a sequence of lines and yields the matching line along with N previous lines of context when found:
'''

#http://pymotw.com/2/collections/deque.html
from collections import deque

def search(lines, pattern, history=5):
    previous_lines = deque(maxlen=history)
    for line in lines:
        if pattern in line:
            yield line, previous_lines
        previous_lines.append(line)

# Example use on a file.
if __name__ == '__main__':
    with open('somefile.txt') as f:
        for line, prevlines in search(f, 'line', 5):
            for pline in prevlines:
                print(pline, end='')
            print(line, end='')
            print('-'*20)