In real world applications, the finally clause is useful for TypeError raised by dividing two strings is not handled by theĮxcept clause and therefore re-raised after the finally > divide ( 2, 1 ) result is 2.0 executing finally clause > divide ( 2, 0 ) division by zero! executing finally clause > divide ( '2', '1' ) executing finally clause Traceback (most recent call last):įile '', line 3, in divide TypeError: unsupported operand type(s) for /: 'str' and 'str'Īs you can see, the finally clause is executed in any event. Statement, the returned value will be the one from theįinally clause’s return statement, not the Again, the exception is re-raised afterĬontinue or return statement, exceptions are notįinally clause will execute just prior to the If the exception is not handled by an exceptĬlause, the exception is re-raised after the finallyĪn exception could occur during execution of an except If an exception occurs during execution of the tryĬlause, the exception may be handled by an exceptĬlause. Points discuss more complex cases when an exception occurs: Not the try statement produces an exception. If a finally clause is present, the finallyĬlause will execute as the last task before the try Goodbye, world! KeyboardInterrupt Traceback (most recent call last): The try statement has another optional clause which is intended toĭefine clean-up actions that must be executed under all circumstances. More information on classes is presented inĬhapter Classes.

Many standard modules define their own exceptions to report errors that may Most exceptions are defined with names that end in “Error”, similar to the Information about the error to be extracted by handlers for the exception. Exceptions should typicallyīe derived from the Exception class, either directly or indirectly.Įxception classes can be defined which do anything any other class can do, butĪre usually kept simple, often only offering a number of attributes that allow Programs may name their own exceptions by creating a new exception class (seeĬlasses for more about Python classes). Traceback (most recent call last):įor more information about chaining mechanics, see Built-in Exceptions. May name multiple exceptions as a parenthesized tuple, for example: Not in other handlers of the same try statement. Handlers only handle exceptions that occur in the corresponding try clause, If an exception occurs which does not match the exception named in the exceptĬlause, it is passed on to outer try statements if no handler isįound, it is an unhandled exception and execution stops with a message asĪ try statement may have more than one except clause, to specify Then, if its type matches the exception named after theĮxcept keyword, the except clause is executed, and then execution If an exception occurs during execution of the try clause, the rest of theĬlause is skipped. If no exception occurs, the except clause is skipped and execution of the įirst, the try clause (the statement(s) between the try and x = int ( input ( 'Please enter a number: ' )). Is signalled by raising the KeyboardInterrupt exception. Whatever the operating system supports) note that a user-generated interruption Look at theįollowing example, which asks the user for input until a valid integer has beenĮntered, but allows the user to interrupt the program (using Control- C or It is possible to write programs that handle selected exceptions. Traceback listing source lines however, it will not display lines read fromīuilt-in Exceptions lists the built-in exceptions and their meanings.

Occurred, in the form of a stack traceback. The preceding part of the error message shows the context where the exception The rest of the line provides detail based on the type of exception and what StandardĮxception names are built-in identifiers (not reserved keywords). This is true for all built-in exceptions, but need not be trueįor user-defined exceptions (although it is a useful convention). The string printed as the exception type is the name of the built-in exception The example are ZeroDivisionError, NameError and TypeError. Exceptions come inĭifferent types, and the type is printed as part of the message: the types in The last line of the error message indicates what happened. 10 * ( 1 / 0 ) Traceback (most recent call last):įile '', line 1, in ZeroDivisionError: division by zero > 4 + spam * 3 Traceback (most recent call last):įile '', line 1, in NameError: name 'spam' is not defined > '2' + 2 Traceback (most recent call last):įile '', line 1, in TypeError: can only concatenate str (not 'int') to str

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