Python Exception Classes

There are several exceptions available as part of Python language that are called built-in exceptions. In the same way, the programmer can also create his own exceptions called user-defined exceptions.

This Table summarizes some important built-in exceptions in Python. Most of the exception class names end with the word 'Error'.

Python Built-in Exceptions

Exception Class Name	Description
Exception	Represents any type of exception. All exceptions are sub classes of this class.
ArithmeticError	Represents the base class for arithmetic errors like OverflowError,ZeroDivisionError,FloatingPointError.
AssertionError	Raised when an assert statement gives error.
AttributeError	Raised when an attribute reference or assignment fails.
EOFError	Raised when input() function reaches end of file condition without reading any data.
FloatingPointError	Raised when a floating point operation fails.
GeneratorExit	Raised when generator's close() method is called.
IOError	Raised when an input or output operation failed. It raises when the file opened is not found or when writing data disk is full.
ImportError	Raised when an import statement fails to find the module being imported.
IndexError	Raised when a sequence index or subscript is out of range.
KeyError	Raised when a mapping (dictionary) key is not found in the set of existing keys.
KeyboardInterrupt	Raised when the user hits the interrupt key(normally control-C or Delete).
NameError	Raised when an identifier is not found locally or globally.
NotImplementedError	Derived from 'RuntimeError'. In user defined base classes,abstract methods should raise this exception when they require derived classes to override the method.
OverflowError	Raised when the result of an arithmetic operation is to large too be represented. This cannot occur for long integers (which would rather raise 'MemoryError').
RuntimeError	Raised when an error is detected that doesn't fall in any of the other categories.
StopIteration	Raised by an iterator's next() method to signal that there are no more elements.
SyntaxError	Raised when the compiler encounters a syntax error.Import or exec statements and input() and eval() functions may raise this exception.
IndentationError	Raised when indentation is not specified properly.
SystemExit	Raised by the sys.exit() function. When it is not handled, the Python interpreter exits.
TypeError	Raised when an operation or function is applied to an object of inappropriate datatype.
UnboundLocalError	Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable.
ValueError	Raised when a built-in operation or function receives an argument that has right datatype but wrong value.
ZeroDivisionError	Raised when the denominator is zero in adivision or modulus operation.

Python Exception Handling Example for User Date

#example for syntax error 
try: 
   date = eval(input("Enter date:")) 
except SyntaxError: 
   print('Invalid date entered') 
else: 
   print('You entered:', date)
A Python program to handle IOError produced by open() function. 
#example for IOError #accept a filename 
try: 
   name = input('Enter filename:') 
   f = open(name, 'r') 
except IOError: 
   print('File not found:', name) 
else: 
   n = len(f.readlines()) 
   print(name, 'has', n, 'lines') 
   f.close()

Python Example to Handle Multiple Exceptions

#a function to find total and average of list elements 
def avg(list): 
   tot=0 
   for x in list: 
      tot+=x 
   avg = tot/len(list) 
   return tot, avg 
#call the avg() and pass a list 
try: 
   t,a = avg([1,2,3,4,5,'a']) 
#here, give empty list and try. 
   print('Total= {}, Average= {}'.format(t,a)) 
except TypeError: 
   print('Type Error, please provide numbers.') 
except ZeroDivisionError: 
   print('ZeroDivisionError, please do not give empty list.')