ex20.py

from sys import argv

script, input_file = argv

def 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=1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)