常见异常，更多异常用法，抛出异常

1，异常

try:
  open('abc.txt','r')
    print(a)
  except BaseException as msg:
    print(msg)

2，更多异常用法

try:
  a = '异常测试：'
  print(a)
except NameError as msg:
  print(msg)
else:
  print('没有异常时执行')

# 不管是否出现异常，都会执行
try:
  print(a)
except NameError as msg:
  print(msg)
finally:
  print('不管是否出现异常，都会被执行')

3，抛出异常

#定义 say_hello() 函数

def say_hello(name=None):
  if name is None:
​    raise NameError('"name" cannot be emoty')
  else:
​    print('hello, %s' %name)

# 调用say_hello () 函数
# say_hello()