01. unusual concept
Program at run time, if the Python interpreter encounters an error, stop program execution, and prompts some wrong information , which is abnormal
The program stops executing and an error message this action, we usually call: throw (raise) abnormal
When developing the program, it is difficult for all of the special circumstances everything is handled by abnormal capture can be done centralized process for emergencies, so as to ensure program stability and robustness
02. catch the exception
2.1 simple catch exceptions grammar
Program development, if the execution of some code can not be determined correctly , can increase the try (try) to catch the exception
Catch exceptions simplest syntax:
try try , try to write the code below, uncertain whether the code can be executed normally
except if not , write code below attempt fails
Simple exception catching drills - requires the user to enter an integer
2.2 type of error trapping
During program execution, you may encounter different types of exceptions , and the need for different types of exceptions, respond differently , this time, we need to capture the type of error
The syntax is as follows:
When the Python interpreter throws an exception , the first word in the last line of the error message, type is wrong
Capture exception type exercise - require user input integer
demand
It prompts the user to enter an integer
Integer by using the user input and output 8
Capture unknown error
In the development, to anticipate all possible errors , or have some difficulty
If you want the program to any error occurs regardless , will not because Python interpreter throws an exception has been terminated , you can add another except
The syntax is as follows:
2.3 abnormal capture the full syntax
In the actual development, in order to be able to deal with complex anomalies, abnormal complete syntax is as follows:
prompt:
Related scenarios complete syntax, in the follow-up study, combined with actual cases will be better understood
Now there is a first impression to this grammatical structure
Code else only when there is no abnormality will be executed
finally, whether or not there is an exception code that will be executed
Prior to the exercise of a complete capture abnormal code is as follows:
03. abnormal transfer
Abnormal transfer - when the function / method execution exception occurs , it will pass the exception to the function / method call party
If the transfer to the main program , still no exception handler , the program will be terminated
prompt
In development, may increase in the main function abnormalities capture
The other function calls in the main function, as long as the abnormal, will be passed to the main function abnormalities captured in
This eliminates the need in the code to increase the number of exception traps , to ensure clean code
demand
The demo1 defined function () prompts the user and returns an integer
Defined functions demo2 () call demo1 ()
Demo2 call in the main ()
04. throws raise an exception
4.1 application scenarios
In development, in addition to code execution error Python interpreter throws than an exception
But also according to the application -specific business needs active thrown
Examples
The user is prompted to enter a password , if the length is less than 8 , throws an exception
note
The current function is only responsible for prompting the user for a password if the password length is incorrect, other functions require additional processing
So you can throw an exception , the other functions need to be addressed catch the exception
4.2 throws an exception
Exception provides a Python exception class
In the development, if they meet a specific business need , you want to throw an exception , you can:
Creating an Exception of objects
Using the raise keyword thrown exception object
demand
Input_password defined function, the user is prompted to enter a password
If the user inputs the length <8, an exception is thrown
If the user inputs the length> = 8, returns the input password
