Python - Built-in Exceptions

Python From Beginner to Advanced

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Python provides a number of built-in exceptions that handle different error cases. Understanding these exceptions is crucial for effective error handling and robust Python programming. Below is a table of some common built-in exceptions with rephrased descriptions, followed by examples demonstrating how to handle a couple of these exceptions.

#	Exception	Description
1	BaseException	The superclass for all exceptions, serving as the base class for all other exceptions.
2	StopIteration	Triggered when an iterator's next() method signals that there are no further items.
3	SystemExit	Triggered by calling sys.exit(), signaling the interpreter to exit.
4	StandardError	Obsolete in Python 3, it was the base class for all built-in exceptions except StopIteration and SystemExit.
5	ArithmeticError	Superclass for exceptions that occur for errors in numeric calculations.
6	OverflowError	Occurs when a calculation exceeds a numeric type's designated limit.
7	FloatingPointError	Occurs when a floating point operation fails.
8	ZeroDivisionError	Occurs when division or modulo operation is performed with zero as the divisor.
9	AssertionError	Triggered when an assert statement fails.
10	AttributeError	Occurs when attribute reference or assignment fails.
11	EOFError	Triggered when no input is detected from input() or raw_input() and EOF is reached.
12	ImportError	Occurs when an import statement fails to find the module definition or cannot load it.
13	KeyboardInterrupt	Triggered when the user interrupts program execution, typically with a Ctrl+C.
14	LookupError	Base class for errors that occur during a lookup.
15	IndexError	Triggered when an index is not found in a sequence.
16	KeyError	Occurs when a dictionary key is not found during lookup.
17	NameError	Triggered when a local or global name is not found.
18	UnboundLocalError	Occurs when a reference is made to a local variable in a function or method but no value has been assigned to it.
19	EnvironmentError	Obsolete in Python 3; use OSError instead. Base class for I/O related errors.
20	IOError	Obsolete in Python 3; integrated into OSError. Triggered for errors related to I/O operations.
21	OSError	Errors related to system operations, encompasses the OS-related errors.
22	SyntaxError	Triggered by parser encountering a syntax error.
23	IndentationError	A subclass of SyntaxError, triggered by incorrect indentation.
24	SystemError	Raised when the interpreter detects an internal error.
25	SystemExit	Raised when sys.exit() is called.
26	TypeError	Raised when an operation or function is applied to an object of inappropriate type.
27	ValueError	Raised when a function receives an argument of correct type but inappropriate value.
28	RuntimeError	An error that doesn't fall into any other category, typically used for general runtime errors.
29	NotImplementedError	Raised to indicate that an abstract method requires an overridden implementation in a subclass.

Example 1: Handling KeyError

This example demonstrates handling a KeyError, which occurs when a requested key is not found in a dictionary.

Python3

. . . .

Explanation:

The dictionary my_dict only contains keys for 'name' and 'age'.
Attempting to access my_dict['address'] raises a KeyError because the 'address' key does not exist.
The except KeyError block catches this specific error and prints a message indicating the key is missing.

Example 2: Handling IndexError

This example shows how to handle an IndexError, which is raised when attempting to access an index that is out of the range of a list.

Python3

. . . .

Explanation:

my_list is defined with three elements: indexes 0, 1, and 2.
Attempting to access my_list[5] raises an IndexError because there is no element at index 5.
The except IndexError block is used to catch the error and inform the user that they have tried to access a non-existent list index.

Understanding and properly handling these exceptions are vital for developing dependable and user-friendly Python applications. This approach ensures your program can gracefully handle errors and provide informative feedback to users, improving both usability and reliability.

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