Exceptions to Python's learning notes

Python uses an exception object to represent the exception, and if the exception object is not processed or snapped, the program will backtrack (traceback) execution.

Exceptions can be raised automatically when an error occurs, or they can be raised proactively.

If the exception is thrown, it is propagated to the program call where it is not processed, until the main program (global scope), and if the main program still has no exception handling, the program terminates with a stack trace.

Raise: Throwing an exception

Raise Exceptiontraceback (most recent):   " <pyshell#1> "  in <module>    raise  exceptionexception

>>> Raise Exception ("Error!!!")
Traceback (most recent):
File "<pyshell#2>", line 1, in <module>
Raise Exception ("Error!!!")
Exception:error!!!

Common built-in exception classes:

Class name	Describe
Exception	base class for all exceptions
Attributeerror	Thrown when an attribute reference or assignment fails
IOError	Thrown when an attempt is made to open a file that does not exist (including other conditions)
Indexerror	Thrown when using an index that does not exist in the sequence
Keyerror	Thrown using a key that does not exist in the map
Nameerror	Thrown when a name (variable) cannot be found
SyntaxError	Thrown when the code is in the wrong form
TypeError	Object raised in the built-in operation or function applied to the wrong type
ValueError	The built-in operation or function is applied to the correct object, but the object uses an inappropriate value to raise the
Zerodivision	The second argument of the division or modulo-division operation is a 0 o'clock throw

Custom exception class: Inherit from exception

class Defexception (Exception):Pass

Catching exceptions: Using the Try/except statement implementation >>> try:

    =  int (input ("the firstnum:"))    = Int (input ("thesecond Num:"))    print(x/y)except  Zerodivisionerror:    print("Error") the first    num :5 Thesecond num:0
Error

>>>Try: x= Int (Input ("The first num:")) Y= Int (Input ("The second num:"))    Print(x/y)exceptZerodivisionerror:Print("Error")exceptValueError:Print("TypeError") The first num:5The second Num:otypeerror

Catch multiple exceptions with one block:

Try :     =  int (input ("the firstnum:"))    = Int (input ("thesecond Num:"))    print(x/y)except  ( Zerodivisionerror,valueerror):    print("Error") The first    num:5 Thesecond Num:0error

Snapping objects:

Try :     =  int (input ("the firstnum:"))    = Int (input ("thesecond Num:"))    print(x/y)except  ( Zerodivisionerror,valueerror) as E:    print(e) The first    num:5 Thesecond Num:0division by Zero

Catch all Exceptions:

Try :     = Int (Input ("the firstnum:"))    = Int (input ("Thesecond num:  "))    print(x/y)except:      Print("some errors") the first num:5 Thesecond num:some errors 

This approach captures the user's attempt to abort execution and hides any errors that programmers have not thought of and are unprepared for.

To handle exception cases:

#loop when the input is not valid until the legal value exits the loop whileTrue:Try: x= Int (Input ("The first num:")) Y= Int (Input ("The second num:"))        Print(x/y)except:        Print("Error")    Else:         Break#Run ResultsThe first num:5The second num:0errorthe first num:6The second num:32.0

Finally clause: Cleans after possible exceptions, regardless of whether any exceptions are performed. In the same try statement, it cannot be used with except.

x =NoneTry: x= 1/0finally:    Print("Cleaning")    delx#ResultsCleaningtraceback (most recent): File"input.py", Line 4,inch<module>x= 1/0zerodivisionerror:division by ZeroRepl closed***

You can combine try,except,else,finally in one statement

Try :     = 1/0Else:    print("done")  Finally:    print("cleaning")#  Running results cleaning***repl closed***

Exceptions to Python's learning notes