ex20.py

from sys import argv

script, input_file = argv
def print_all(f):
    print(f.read())

def rewind(f):
    f.seek(0)  # you’re moving to the start of the file.

def print_a_line(line_count, f):
    print(line_count, f.readline())  
    # Each time you do f.readline() you’re reading a line from the file and moving the read head 
    # to right after the \n that ends that line.

current_file = open(input_file)
# The readline() function returns the \n that’s in the file at the end of that line. Add a end = ""
# at the end of your print function calls to avoid adding double \n to every line.

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 += 1
print_a_line(current_line, current_file)

current_line += 1
print_a_line(current_line, current_file)