How to read lines from a file in python starting from the end

Question

I need to know how to read lines from a file in python so that I read the last line first and continue in that fashion until the cursor reach\'s the beginning of the file. A

Answer 1

This solution is simpler than any others I've seen.

def xreadlines_reverse(f, blksz=524288):
    "Act as a generator to return the lines in file f in reverse order."
    buf = ""
    f.seek(0, 2)
    pos = f.tell()
    lastn = 0
    if pos == 0:
        pos = -1
    while pos != -1:
        nlpos = buf.rfind("\n", 0, -1)
        if nlpos != -1:
            line = buf[nlpos + 1:]
            if line[-1] != "\n":
                line += "\n"
            buf = buf[:nlpos + 1]
            yield line
        elif pos == 0:
            pos = -1
            yield buf
        else:
            n = min(blksz, pos)
            f.seek(-(n + lastn), 1)
            rdbuf = f.read(n)
            lastn = len(rdbuf)
            buf = rdbuf + buf
            pos -= n

Example usage:

for line in xreadlines_reverse(open("whatever.txt")):
    do_stuff(line)