Introduction to Python Exception Handling
A mechanism provided by Python, like most other object-oriented programming languages, to deal with all possible errors that may generate during the execution of a program code, with the mechanism providing a robust and effective set of methods with every error being handled in the most appropriate manner, technically being facilitated by keywords such as try and except, is termed as Python Exception Handling.
try: Executes when suspicious code is executed
except Exception1: Executed when
exception 1 is raised
except Exception2: Executed when exception 2 is raised
else: If there is no exception then execute this block
Standard Exception List
Exception: All exceptions base class
StopIteration: when no object is pointed by the next method of the iterator this exception is raised
SystemExit: Hoisted through the sys.exit() function.
StandardError: Except StopIteration and SystemExit this acts as the base class for all built-in functions.
ArithmeticError: For all the numeric errors these exceptions act as the base class.
OverflowError: For a numeric type if the calculation exceeds the maximum possible value then this error is raised.
FloatingPointError: Failure of a float operation kicks this error
ZeroDivisionError: Raised when a divide by zero situation occurs in the code
AssertionError: When the assert statement fails then this error is triggered
AttributeError: When an assignment or an attribute reference fails then it raises this error
EOFErroR: Raised when no more input from any of the function and end of file is reached
ImportError: Raised while an import declaration fails.
KeyboardInterrupt: Raised when there is an interrupt to the program execution
LookupError: All lookup errors fall under this base class
IndexError: Raised when index not found
KeyError: Raised when the dictionary does not hold the mentioned key value
NameError: Raised for a missing identifier locally or globally in the program
UnboundLocalError: Raised when using a local variable without any value being assigned to it.
EnvironmentError: Base class for environment-oriented errors which occur outside python
IOError: Raised while an input/ output process be unsuccessful
SyntaxError: All python syntax oriented errors are handled by this exception
IndentationError: Improper indentation will lead to this kind of errors
SystemError: This occurs at a situation when the interpreter doesn’t work as expected, but this error does not make the python program to go out of execution
SystemExit: When sys.exit() function is used by the python interpreter then it leads to this exception. this makes the code abnormally terminate when not been handled properly.
TypeError: When an operation is invalid for a particular data type then this error is prompted
ValueError: When a function holds a valid type argument but an improper value is been specified for that type argument
RuntimeError: If any of the above categories are not satisfied then this error is raised
NotImplementedError: Raised while a nonfigurative method that wants to be put into practice in an inherited class is not in fact implemented. Put in order and managing these exceptions is a process carried out by the except block which is inserted at the end of every try block.
Exception Handling Process in Python
- Except clause with multiple exceptions
- Except clause with no exception mentioned
- Except clause with Arguments
Below we will discuss the Exception Handling Process in Python
1. Except clause with Multiple Exceptions
This allows more than one except statement being declared in one except clause and all of these declared exceptions can be raised from this except clause.
try: Code block1
Executes when one among the exception happens
else: Executed when no exception is raised
2. Except clause with no exception
All the exceptions triggered from the try block are capable of being processed here.
Executes if any type of exception happens
If there is no exception then execute this block
3. Except clause with Arguments
The actual cause of the exception will be held in the argument value
Argument value is printed here
4. Exception handling program
fh = open("testfile1", "w")
print "Going to close the file"
print "Error: can\'t find file or read data"
Every programming language holds the process of raising an exception whenever it faces an unexpected set of situations and python is one among them which produces profound techniques for handling these exceptions which makes it a strong base meted programming language.
This has been a guide to Python Exception Handling. Here we discuss the standard exception list and process along with Syntax. You can also go through our other suggested articles to learn more –