seek()

seek(0)代表从文件头开始，1表示从当前位置开始，2代表从末尾开始

from sys import argvscript, input_file = argvdef print_all(f):    print f.read()def rewind(f):    f.seek(0)def print_a_line(line_count, f):    print line_count, f.readline()current_file = open(input_file)print "First let's print the whole file: \n"print_all(current_file)print "Now let's rewind, kind of like a tape."rewind(current_file)print "Let's print three lines:"current_line = 1print_a_line(current_line, current_file)current_line = current_line + 1print_a_line(current_line, current_file)current_line = current_line + 1print_a_line(current_line, current_file)print "4", current_file.readline()print "5", current_file.readline()current_file.close()

Xavier@Xavier-PC ~/python_test
$ python ex20.py test_20.txt
First let’s print the whole file:

gege
i
love
u

Now let’s rewind, kind of like a tape.
Let’s print three lines:
1

2 gege

3 i

4 love

5 u