from sys import argv
#from os.path import exists
script, input_file = argv
def print_all(f):
print (f.read())
def rewind(f):
f.seek(0) #重定位到文件开头
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)
调用命令：
python .\ex20.py .\ex20_Test.txt
输出结果：
First let's print the whole file:
To all the people out there.
I say I don't like my hair.
I need to shave it off.
Now let's rewind, kind of like a tape.
Let's print three lines:
1 To all the people out there.
2 I say I don't like my hair.
3 I need to shave it off.
