习题20.md

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)