编程读取文件指定行

#编写程序实现读取文件前几行
def print_line(file_name):
    line = int(input('请输入要显示前几行：'))
    f = open(file_name)
    for each_line in range(0,line):
        print(f.readline())

file_name = input('请输入要打开的文件名：')
print_line(file_name)

#编程实现读取指定行

def print_content(file_name,lines):

    (former, latter) = lines.split(':',1)
    if former == '':
        former=1
    if latter == '':
        latter=-1
    former = int(former)
    latter = int(latter)

    if former==1 and latter == -1:
        print('全文内容如下：')
    elif latter == -1:
        print('文件%s从第%d行到文件末尾内容如下：'% (file_name,former))
    elif former == 1:
        print('文件%s从开始到第%d行内容如下：'% (file_name, latter))
    else:
        print('文件%s从第%d行到第%d行的内容如下：' % (file_name, former, latter))

    f = open(file_name)
    for each_line_num1 in range(former-1):
        f.readline()
    if (latter-former+1)< 0:
        print(f.read())
    else:
        for each_line_num2 in range(latter-former+1):
            print(f.readline())

    f.close()
    
file_name = input('请输入要打开的文件:')
lines = input('请输入需要显示的行数【格式如13:21或 ：21 或21:】:')
print_content(file_name,lines)