functions_and_files.py

#!/usr/bin/python

from sys import argv

script, input_file = argv

def print_all(f):
	print f.read()

def rewind(f):
	f.seek(0)
	""" Each time you do seek(0), you move to the start of the file.
	"""

def print_a_line(line_count, f):
	print line_count, f.readline(),
	"""Inside readline() is code that scans each byte of the file 
	until it finds a \n character, then stops reading the file to 
	return what it found so far. The file f is responsible for 
	maintaining the current position in the 
	file after each readline() call, so that it will keep 
	reading each line.
	"""

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 "Now let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

# current_line = current_line + 1
current_line += 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)