Exception handling mechanism

• One 、 exception handling
• Two 、 Exception handling mechanism
• 3、 ... and 、 An exception

One 、 exception handling

1、 Wrong type
ERROR abnormal ： System type error , The cause may be a system crash , Out of memory , It is recommended that the procedure be terminated
Exception abnormal ： Represents an exception that the program can handle , Can capture and possibly recover . This kind of problem can be solved .

2、 Error alert
Possible errors ：

AttributeError .lOError . ImportError . IndexError、SyntaxError、TypeError、ValueError、KeyError、NameError.

Common mistakes are as follows ：

. IndentationError: The indentation error
. KeyboardInterrupt: Ctrl+C Pressed
. UnboundLocalError : There is a global variable with the same name

3、 give an example

1、print(a)
NameError Wrong name , No such parameter
2、print(10/0)
ZeroDivisionError: division by zero The divisor cannot be zero 0
3、with open('hello.txt') as f:
pass
FileNotFoundError file error , There is no such document

Two 、 Exception handling mechanism

try： Try to run the program
except：try Something went wrong with the running code （ There can be more than one ）
else：try There is no problem running the program
finally: Code that will run in any case

give an example
execpt It is to select one from many

try: Try to run
a=1
print(b)
except NameError as name_error: If the name is wrong
print('name_error')
except KeyError as key_error: If the keyword is wrong
print('key_error')
except Exception as all_error: If there is a mistake, then
print('all_error')
finally: In the end, we will implement it uniformly
print(' end ')

3、 ... and 、 An exception

1、raise Throw an exception

age = int(input('age:'))
if 0<age<150:
print(age)
else:
# Throw an exception 
raise ValueError(" Age must be in 0~150 Between ")
# result 
Input 100
ValueError: Age must be in 0~150 Between

2、 Custom exception
Through custom exception

# Custom exceptions 
class AgeError(ValueError): Custom error module ：AgeError, It belongs to ValueError class
pass
age = int(input('age:'))
if 0<age<150:
print(age)
else:
# Throw an exception 
raise AgeError(" Age must be in 0~150 Between ")
# result 
Input 1000
AgeError: Age must be in 0~150 Between
``