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How to pass argument to an Exception in Python?

  • Difficulty Level : Medium
  • Last Updated : 10 May, 2020

There might arise a situation where there is a need for additional information from an exception raised by Python.
Python has two types of exceptions namely, Built-In Exceptions and User-Defined Exceptions.

Why use Argument in Exceptions?
Using arguments for Exceptions in Python is useful for the following reasons:

  • It can be used to gain additional information about the error encountered.
  • As contents of an Argument can vary depending upon different types of Exceptions in Python, Variables can be supplied to the Exceptions to capture the essence of the encountered errors. Same error can occur of different causes, Arguments helps us identify the specific cause for an error using the except clause.
  • It can also be used to trap multiple exceptions, by using a variable to follow the tuple of Exceptions.

Arguments in Buil-in Exceptions:

The below codes demonstrates use of Argument with Built-in Exceptions:

Example 1:






try:
    b = float(100 + 50 / 0)
except Exception as Argument:
    print( 'This is the Argument\n', Argument)

Output:

This is the Argument
 division by zero

Example 2:




my_string = "GeeksForGeeks"
  
try:
    b = float(my_string / 20)
except Exception as Argument:
    print( 'This is the Argument\n', Argument)

Output:

This is the Argument
 unsupported operand type(s) for /: 'str' and 'int'

Arguments in User-defined Exceptions:

The below codes demonstrates use of Argument with User-defined Exceptions:

Example 1:




# create user-defined exception  
# derived from super class Exception 
class MyError(Exception): 
    
    # Constructor or Initializer 
    def __init__(self, value): 
        self.value = value 
    
    # __str__ is to print() the value 
    def __str__(self): 
        return(repr(self.value)) 
    
try
    raise(MyError("Some Error Data")) 
    
# Value of Exception is stored in error 
except MyError as Argument: 
    print('This is the Argument\n', Argument) 

Output:

This is the Argument
 'Some Error Data'

Example 2:




# class Error is derived from super class Exception 
class Error(Exception): 
  
    # Error is derived class for Exception, but 
    # Base class for exceptions in this module 
    pass
  
class TransitionError(Error): 
  
    # Raised when an operation attempts a state 
    # transition that's not allowed. 
    def __init__(self, prev, nex, msg): 
        self.prev = prev 
        self.next = nex 
  
try
    raise(TransitionError(2, 3 * 2, "Not Allowed")) 
  
# Value of Exception is stored in error 
except TransitionError as Argument: 
    print('Exception occurred: ', Argument) 

Output:

Exception occurred:  (2, 6, 'Not Allowed')

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