python学习else,with

else

要么怎样，要么不怎样

干完了能怎样，干不完就别想怎样

if XXX:

　　XXX

else:

　　XXX

def showMaxFactor(num):
    count = num // 2
    while count > 1:
        if num % count == 0:
            print('%d最大的约数是%d' % (num,count))
            break
        count -= 1
    else:
        print('%d是素数' % num)

num = int(input('请输入一个数'))
showMaxFactor(num)

没有问题，那就干吧

try:
    int('abc')
except ValueError as reason:
    print('出错')
else:
    print('没错')

with

不使用with时

try:
   f = open('data.txt','w')
   for each_line in f:
       print(each_line)
except OSError as reason:
    print('出错'+ str(reason))
finally:
    f.close()

使用with时，会在异常时自动关闭文件f.close

try:
   with open('data.txt','w') as f
       for each_line in f:
           print(each_line)
except OSError as reason:
    print('出错'+ str(reason))