exercise 20

from sys import argv

script, input_file = argv

# 定义print_all函数
def print_all(f):
    # 打印文件全部内容
    print(f.read())

# 定义函数rewind,参数f引用文件对象
def rewind(f):
    # f。seek(0)是让基准点回到开始位置
    # 如果是seek(1),那就是让基准点回到当前位置
    # 如果是seek(2),那就是让基准点回到结束为止
    f.seek(0)

# 定义函数print_a_line,参数line_count和f都是引用文件对象的
def print_a_line(line_count, f):
    #f.readline()是一行一行读取的
    print(line_count, f.readline())

#  把文件input_file对象赋值给current_file
current_file = open(input_file)

# 打印
print("First let's print the whole file:\n")

# 调用函数print_all
print_all(current_file)

# 打印
print("Now let's rewind, kind of like a tape.")

# 调用函数rewind,作用就和倒带差不多
rewind(current_file)

# 打印
print("Let's print three lines:")

# 把1赋值给current_line
current_line = 1
# 调用函数print_a_line
print_a_line(current_line, current_file)

# current_line自增
current_line = current_line + 1
# 调用print_a_line函数
print_a_line(current_line, current_file)

# 自增
current_line = current_line + 1
# 调用函数print_a_line
print_a_line(current_line, current_file)

第一次print_a_line被调用, current_line被赋值1
第二次print_a_line被调用, current_line被赋值2
第三次print_a_line被调用, current_line被赋值3

4.点击
5.点击