(Python) exception handling try...except, raise

Reprinted from Https://www.cnblogs.com/Lival/p/6203111.html

(Python) exception handling try...except, raise First, try...except Sometimes when we write a program, there are some errors or exceptions that cause the program to terminate. For example, when division is done, the divisor is 0, which causes a zerodivisionerror Example: ? 1234 a=10b=0c=a/bprint"done" Operation Result: Traceback (most recent): File "c:/users/lirong/pycharmprojects/untitled/openfile.py", line 3, <module> C=a/b Zerodivisionerror:integer division or modulo by zero We found that the program was interrupted because of Zerodivisionerror, and the statement print "done" was not running. To handle the exception, we use Try...except to change the code: ? 12345678 a=10b=0try:    c=a/b    print cexcept ZeroDivisionError,e:    print e.messageprint "done" 　　 Operation Result: Integer division or modulo by zero Done This way, the program does not break because of an exception, and the print "done" statement executes normally. We put statements that could have errors in the Try module and use except to handle exceptions. Except can handle a specialized exception, or it can handle an exception in a set of parentheses, and if no exception is specified after except, all exceptions are handled by default. Every try must have at least one except Handling a set of exceptions can be written like this (where E represents an instance of the exception): ? 1234 try：    passexcept(IOError ,ZeroDivisionError),e:    printe Try .... except...else statement, when no exception occurs, the statement in else is executed. Example: ? 12345678910 a=10b=0try:    c = b/ a    print cexcept (IOError ,ZeroDivisionError),x:    print xelse:    print "no error"print "done" Operation Result: 0 No error Done Second, raise throws an exception Example: If the input data is not an integer, a valueerror is raised ? 12345 inputValue=input("please input a int data :")iftype(inputValue)!=type(1):    raise ValueErrorelse:    printinputValue Suppose you enter 1.2 and run the result as: Please input a int data:1.2 Traceback (most recent): File "c:/users/lirong/pycharmprojects/untitled/openfile.py", line 3, <module> Raise ValueError ValueError If you enter 1, the result of the operation is: Please input a int data:1 1 Third, try ... finally The statements in finally are executed, regardless of whether the exception occurred or not, until the end of the program. ? 123456 a=10b=0try:    printa/bfinally:    print"always excute" Operation Result: Traceback (most recent): Always Excute File "c:/users/lirong/pycharmprojects/untitled/openfile.py", line 4, <module> Print A/b Zerodivisionerror:integer division or modulo by zero Although an exception occurs, the statements in finally can be executed normally before the program terminates. The finally statement can also be used with the except statement. ? 12345678 a=10b=0try:    printa/bexcept:    print "error"finally:    print"always excute" Operation Result: Error Always Excute Iv. Customizing an Exception class Customize a MyException class, inheriting exception. ? 1234 classMyException(Exception):    def__init__(self,message):        Exception.__init__(self)        self.message=message    If the number entered is less than 10, a MyException exception is thrown: ? 123456 a=input("please input a num:")if a<10:    try:        raise MyException("my excepition is raised ")    except MyException,e:        print e.message 　　 Operation Result: Please input a num:1 My excepition is raised Five, Python all the standard exception class: Exception name Description Baseexception base class for all exceptions Systemexit Interpreter Request exited Keyboardinterrupt User interrupt execution (usually input ^c) Exception base class for general errors Stopiteration There are no more values for iterators Generatorexit Generator (generator) exception occurred to notify exit Systemexit Python Interpreter Request Exit StandardError Base class for all built-in standard exceptions Arithmeticerror base class for all numeric calculation errors Floatingpointerror Floating-point calculation error Overflowerror Numeric operation exceeds maximum limit Zerodivisionerror Except (or modulo) 0 (all data types) Assertionerror Assertion statement failed Attributeerror Object does not have this property Eoferror No built-in input, EOF Mark reached EnvironmentError Base class for operating system errors IOError Input/output operation failed OSError Operating system error Windowserror System call failed Importerror Failed to import module/object Keyboardinterrupt User interrupt execution (usually input ^c) Lookuperror base class for invalid data queries Indexerror There is no such index (index) in the sequence Keyerror This key is not in the map Memoryerror Memory overflow error (not fatal for Python interpreter) Nameerror Object not declared/initialized (no attributes) Unboundlocalerror To access uninitialized local variables Referenceerror Weak references (Weak reference) attempt to access objects that have been garbage collected RuntimeError General run-time errors Notimplementederror Methods that have not been implemented SyntaxError Python syntax error Indentationerror Indentation Error Taberror Tab and Space Mix Systemerror General Interpreter system error TypeError An operation that is not valid for type ValueError Invalid parameter passed in Unicodeerror Unicode-related errors Unicodedecodeerror Error in Unicode decoding Unicodeencodeerror Unicode encoding Error Unicodetranslateerror Unicode Conversion Error Warning Base class for warnings Deprecationwarning Warnings about deprecated features Futurewarning Warning about the change in the construction of future semantics Overflowwarning Old warning about auto-promotion to Long integer Pendingdeprecationwarning Warnings about attributes that will be discarded Runtimewarning Warning for suspicious run-time behavior (runtime behavior) Syntaxwarning Warning of suspicious syntax Userwarning Warnings generated by user code

(Python) exception handling try...except, raise