ex20.py

#!/bin/python2
# -*- coding: utf-8 -*-

# ex20: Functions and Files

# Import argv variables from the sys module
from sys import argv

# Assign the first and the second arguments to the two variables
script, input_file = argv

# Define a function called print_call to print the whole contents of a
# file, with one file object as formal parameter
def print_all(f):
    # print the file contents
    print f.read()


# Define a function called rewind to make the file reader go back to
# the first byte of the file, with one file object as formal parameter
def rewind(f):
    # make the file reader go back to the first byte of the file
    f.seek(0)


# Define a function called print_a_line to print a line of the file,
# with a integer counter and a file object as formal parameters
def print_a_line(line_count, f):
    # Test whether two variables are carrying the same value
    print "line_count equal to current_line?:", (line_count == current_line)
    # print the number and the contents of a line
    print line_count, f.readline()


# Open a file
current_file = open(input_file)

# Print "First let's print the whole file:"
print "First let's print the whole file:\n"

# call the print_all function to print the whole file
print_all(current_file)

# Print "Now let's rewind, kind of like a tape."
print "Now let's rewind, kind of like a tape."

# Call the rewind function to go back to the beginning of the file
rewind(current_file)

# Now print three lines from the top of the file

# Print "Let's print three lines:"
print "Let's print three lines:"

# Set current line to 1
current_line = 1
print "current_line = %d" % current_line
# Print current line by calling print_a_line function
print_a_line(current_line, current_file)

# Set current line to 2 by adding 1
current_line += 1
print "current_line is equal to:%d" % current_line
# Print current line by calling print_a_line function
print_a_line(current_line, current_file)

# Set current line to 3 by adding 1
current_line += 1
print "current_line is equal to:%d" % current_line
# Print current line by calling print_a_line function
print_a_line(current_line, current_file)