异常处理

异常处理：

例1：
　　data1 = {}
　　data2 = []
try:
　　print(data2[1])
　　data1["name"]
except KeyError as e:
　　print("no key:", e)
except IndexError as e:
　　print("list index error:", e)

 

等同：

data1 = {}
data2 = []
try:
　　print(data2[1])
　　data1["name"]
except(KeyError, IndexError) as e:
　　print("no key:", e)
   
   
例2：except Exception  所有的错误都可以抓：不建议用
  
try:
　　print(data2[1])
　　data1["name"]
except Exception as e:
　　print("no key:", e)
  
例3：
data1 = {"name":"brace"}
data2 = [1,2]
try:
　　print(data2[1])
　　data1["name"]
except KeyError as e:
　　print("no key:", e)
except IndexError as e:
　　print("list index error:", e)
except Exception as e:
　　print("no key:", e)
else:
　　print("一切正常才执行")
finally:
　　print("不管有没错都执行")
    

自定义异常：
 
class BraceException(Exception):
def __init__(self, msg):
   self.message = msg
 
def __str__(self):
　　return self.message
try:
　　raise BraceException("数据库连接不上！")
except BraceException as e:
  　　print(e)
 
 输出：
  　　数据库连接不上！
  
  
 class BraceException(Exception):
 
  def __init__(self, msg):
   self.message = msg
 
  def __str__(self):
   return "XXXXXXXXXXXX"
 try:
  raise BraceException("数据库连接不上！")
 except BraceException as e:
  print(e)
 
 输出：
  XXXXXXXXXX