# Example of a generator with extra state that can be
# accessed.   Simply define as a class!

from collections import deque

class linehistory:
    def __init__(self, lines, histlen=3):
        self.lines = lines
        self.history = deque(maxlen=histlen)

    def __iter__(self):
        for lineno, line in enumerate(self.lines,1):
            self.history.append((lineno, line))
            yield line

    def clear(self):
        self.history.clear()

with open('somefile.txt') as f:
     lines = linehistory(f)
     for line in lines:
         if 'python' in line:
             for lineno, hline in lines.history:
                 print('{}:{}'.format(lineno, hline), end='')