Python-exception Handling

first, Abnormal

What is an exception?

Is the event that affects the normal execution of the program, the exception occurs during the execution of the program, when the script is abnormal, we need to capture it, or the program Terminates.

Exception handling:

1. Catch exception: try: ... except .....

1  whileTrue:2     Try:3Num1=input ('>>:')4num2 = input ('>>:')5Num1=int (num1)#error, no longer executes the code block inside the try, directly into the except6num2 =int (num2)7num=num1+num28         Print(num)9     exceptException as E:Ten         Print(e)#capture Error message program Re-execution

2. Complex exception handling Structure:

Try

Code Block 1

Except

Code Block 2

Else

Code block 3

Finally

Code Block 4

No exception: 1-3-4

Out Exception: 1-2-4

3. Abnormal type

Exception can catch all the exceptions

Other common exceptions

1 Attributeerror attempts to access a tree that does not have an object, such as foo.x, but Foo has no attribute x2IOError input/output exception: basically, The file cannot be opened3 Importerror cannot introduce modules or packages; it is basically a path problem or a name error4 indentationerror syntax error (subclass); code not aligned correctly5The indexerror index exceeds the sequence boundary, for example, when X has only three elements, but tries to access the X[5]6 Keyerror attempts to access keys that do not exist in the dictionary7Keyboardinterrupt Ctrl +C is pressed8 Nameerror using a variable that has not been assigned to an object9 syntaxerror python code is illegal, code can not compile (personally think this is a syntax error, write Wrong)Ten TypeError Incoming object types are not compliant with the requirements one Unboundlocalerror attempts to access a local variable that has not yet been set, basically because there is another global variable with the same Name. a cause you think you're accessing it -ValueError Pass in a value that is not expected by the caller, even if the value is of the correct type

exceptions for special handling or reminders need to be defined first, and finally defined exception to ensure that the program runs correctly

1S1 ='Hello'2 Try:3 int (s1)4 exceptIndexerror as E:5     Printe6 exceptKeyerror as E:7     Printe8 exceptValueError as E:9     PrinteTen exceptException as E: one     PrintE

proactively triggering exceptions

Raise ........

1  whileTrue:2     Try:3Num1=input ('>>:')4num2 = input ('>>:')5num1=int (num1)6num2 =int (num2)7num=num1+num28         Print(num)9         RaiseException ('eeeeeeeeeerrrrrrrrrrrrrrssssssss')#proactively triggering exceptionsTen     exceptException as E: one         Print(e)#Print out Eeeeeeeeeerrrrrrrrrrrrrrssssssss

Assertion : Assert condition

1 Print (1) 2 assert 1==13print(2)4" output: 15          26"

second, Reflection

  1, allowing users to enter different urls:  
  account/ Login  
  account/logout  
  Home/index  
  home/order  
  2, see different results  
  3, Enter a URL that does not exist, exposure 404 error  
 
 Span style= "font-size:15px" >url list =[account/login,account/logout,home/index,home/order]  
  above URL functions are saved in the account script under controller  
  
 inp=input (' Please enter URL ')  
 m,n=inp.split ('/') #m = Account N=login  
  Go to a module to find a function, if the function exists on the execution function, if there is no function to error  
 getattr () #专门用来去某个地方获取内部的东西 (obtained as a String)  

1  fromControllerImportAccount#The functions of the above URLs are stored in the account script under the controller2 3H=hasattr (account,'Login1')#go to account module (script), whether the login function exists4 Print(h)#presence returns True no return false exists5GetAttr (account,'Login')#go to the account module (script) to get the login function6 7SetAttr (account,'Login1','DDD')#Add the Login1 function to the account module (script)8H=hasattr (account,'Login1')#again to determine if the Login1 attribute exists9 Print(h)#returns TrueTen  oneDelattr (account,'Login1')#Remove the Login1 function from the account module (script) aH=hasattr (account,'Login1')#again to determine if the Login1 attribute exists - Print(h)#returns false

Hasattr (container, ' name ') to determine whether an object contains a specified property in the form of a string

GetAttr (container, ' name ') to get the specified property in the form of a string to an object

SetAttr (container, ' name ', Value) sets the specified property in the form of a string to an object

Delattr (container, ' name ') removes the specified property from an object in the form of a string

Python-exception Handling