异常处理

断言

assert 条件：条件为假时弹出异常AssertionError

try-except

try:
    检测范围
except Exception[ as reason]:
    出现异常(Exception)后的处理代码

例：

try:
    f = open('test.txt')
    print(f.read())
    f.close()
except OSError as reason:
    print('文件出错，原因是：' + str(reason))

try-finally

如果try中没有错误，则跳过except执行finally；如果try中有错误，则先执行except再执行finally。

try:
    f = open('test.txt')
    print(f.read())
    sum = 1 + '1'
except:
    print('出错了')
finally:
    f.close()

raise()

抛出一个异常
raise ZeroDivisionError
raise ZeroDivisionError('除数不能为0')

with

with会自动关闭文件

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