Python file read/write sample

read_write_sample.py

with open(file_name, mode='r+b') as f:
    f.seek(-200,  2)    # seek from the end
    d = f.read(200)     # read from current pos
    f.seek(0)           # seek to begin
    f.write(d)          # write to current pos
    f.seek(-200, 2)     # seek from the end
    f.truncate()        # truncate at current pos