from sys import argv
script,input_file = argv

def print_all(f):
    print(f.read())
def rewind(f):
    #从第一个字符开始，遇到\n算一行
    f.seek(0)
def print_a_line(line_count,f):
    print(line_count,f.readline(),end="")

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:\n")
rewind(current_file)
print("Let's print three lines:\n")
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)


