Introduction to exceptions in python, python Introduction

Introduction to exceptions in python, python Introduction

Each exception is a type of instance, which can be thrown and captured in many ways, so that the program can catch and handle errors.

>>> 1/0Traceback (most recent call last):  File "<pyshell#0>", line 1, in <module>    1/0ZeroDivisionError: integer division or modulo by zero

Exception Handling

You can use the try/try t statement to catch exceptions.

>>> def inputnum():    x=input('Enter the first number: ')    y=input('Enter the first number: ')    try:        print x/y    except ZeroDivisionError:        print "The second number can't be zero"        >>> inputnum()Enter the first number: 10Enter the first number: 0The second number can't be zero

Raise trigger exception

>>> class Muff:    muffled=False    def calc(self,expr):        try:            return eval(expr)        except ZeroDivisionError:            if self.muffled:                print 'Division by zero is illegal'            else:                raise            >>> c=Muff()>>> c.calc(10/2)Traceback (most recent call last):  File "<pyshell#33>", line 1, in <module>    c.calc(10/2)  File "<pyshell#31>", line 5, in calc    return eval(expr)TypeError: eval() arg 1 must be a string or code object>>> c.calc('10/2')5>>> c.calc('1/0')Traceback (most recent call last):  File "<pyshell#35>", line 1, in <module>    c.calc('1/0')  File "<pyshell#31>", line 5, in calc    return eval(expr)  File "<string>", line 1, in <module>ZeroDivisionError: integer division or modulo by zero>>> c.muffled=True>>> c.calc('1/0')Division by zero is illegal

Multiple exception types

try:    x=input('Enter the first number:')    y=input('Enter the seconed number:')    print x/yexcept ZeroDivisionError:    print "The second number can't be zero!"except TypeError:    print "That wasn't a number,was it?"

Capture multiple exceptions at the same time

try:    x=input('Enter the first number:')    y=input('Enter the seconed number:')    print x/yexcept(ZeroDivisionError,TypeError,NameError):    print 'Your numbers were bogus...'

Object capturing

try:    x=input('Enter the first number:')    y=input('Enter the seconed number:')    print x/yexcept(ZeroDivisionError,TypeError),e:    print e    Enter the first number:1Enter the seconed number:0integer division or modulo by zero

Catch all exceptions

try:    x=input('Enter the first number:')    y=input('Enter the seconed number:')    print x/yexcept:    print 'something wrong happened...'    Enter the first number:something wrong happened...