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.

SyntaxError exception class

CopiedCopy Code

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

Handle Multiple Exception classes

CopiedCopy Code

#a function to find total and average of list elements 
def avg(list): 
   for x in list: 
   avg = tot/len(list) 
   return tot, avg 
#call the avg() and pass a list 
   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.')