python head, tail and backward read by lines of a text file

Question

How to implement somethig like the \'head\' and \'tail\' commands in python and backward read by lines of a text file?

Answer 1

Tail:

def tail(fname, lines):
    """Read last N lines from file fname."""
    f = open(fname, 'r')
    BUFSIZ = 1024
    f.seek(0, os.SEEK_END)
    fsize = f.tell()
    block = -1
    data = ""
    exit = False
    while not exit:
        step = (block * BUFSIZ)
        if abs(step) >= fsize:
            f.seek(0)
            exit = True
        else:
            f.seek(step, os.SEEK_END)
        data = f.read().strip()
        if data.count('\n') >= lines:
            break
        else:
            block -= 1
    return data.splitlines()[-lines:]