Understanding Errors and Exceptions in Python Errors and exceptions are fundamental concepts in Python programming that help developers manage unexpected situations and ensure robust application performance. This guide provides a comprehensive overview of errors and exceptions, their types, and best practices for handling them effectively. What Are Errors? Errors are issues that occur during the execution of a program, causing it to stop functioning correctly. They can be broadly categorized into two main types: Syntax Errors: These occur when the code violates the rules of the Python language. Syntax errors are detected at compile time, preventing the program from running. Example: python Run Copy code print("Hello, World!" # Missing closing parenthesis Runtime Errors: These occur during the execution of the program, often due to invalid operations or unexpected conditions. Runtime errors can lead to program crashes if not handled properly. Example: python Run Copy code result = 10 / 0 # ZeroDivisionError What Are Exceptions? Exceptions are a specific type of runtime error that disrupts the normal flow of a program. They provide a way to signal that an error has occurred and can be caught and handled gracefully. Python has a built-in mechanism for managing exceptions, allowing developers to write more resilient code. Common Built-in Exceptions ValueError: Raised when a function receives an argument of the right type but an inappropriate value. TypeError: Raised when an operation or function is applied to an object of an inappropriate type. IndexError: Raised when trying to access an index that is out of range in a list or tuple. KeyError: Raised when a dictionary key is not found. FileNotFoundError: Raised when trying to access a file that does not exist. Exception Handling in Python Python provides a robust mechanism for handling exceptions using try, except, else, and finally blocks: Try Block: Contains the code that may raise an exception. Except Block: Catches and handles the exception if it occurs. Else Block: Executes if the try block does not raise an exception. Finally Block: Executes regardless of whether an exception occurred, often used for cleanup actions. Example: python Run Copy code try: value = int(input("Enter a number: ")) except ValueError: print("That's not a valid number!") else: print("You entered:", value) finally: print("Execution complete.") Best Practices for Error and Exception Handling Be Specific: Catch specific exceptions rather than using a generic except clause to avoid masking other issues. Log Errors: Implement logging to capture error details for debugging and analysis. Use Custom Exceptions: Define custom exception classes for more meaningful error handling in complex applications. Graceful Degradation: Ensure that your application can continue to function or provide useful feedback even when errors occur.

1. ERRORS AND EXCEPTIONS
NKOSANA NXUMALO
241FA01089
BIOTECHNOLOGY

2. DEFINITIONS AND EXAMPLES
• Errors: Problems in a program that cause it to stop execution. They
can be categorized into:
• Syntax Errors: Occur when the code does not follow the correct syntax.
• Runtime Errors: Happen during execution, often due to invalid operations.
• Exceptions: Special conditions that change the normal flow of
execution. They can be handled using specific constructs in Python.

3. SYNTAX ERRORS
• Occur when the code is not written correctly.
• Example:
if x > 10
print("x is greater than 10") # Missing colon

4. RUNTIME ERRORS/LOGICAL ERRORS
• Occur during execution, such as dividing by zero or accessing an out-
of-bounds index.
• Example:
result = 10 / 0 # ZeroDivisionError

5. COMMON BUILT IN EXCEPTIONS
• BaseException: Base class for all exceptions.
• AttributeError: Invalid attribute reference.
• EOFError: input() hits end-of-file.
• FloatingPointError: Floating-point operation fails.
• ImportError: Module not found.
• IndexError: Sequence index out of range.
• KeyError: Dictionary key not found.
• KeyboardInterrupt: User interrupts (Ctrl+C).
• MemoryError: Operation runs out of memory.
• ZeroDivisionError: Division by zero.

6. Contie…..
NameError: Variable not found.
• OverflowError: Arithmetic result too large.
• RuntimeError: General error not categorized.
• SyntaxError: Parsing error.
• IndentationError: Incorrect indentation.
• TabError: Inconsistent tabs/spaces.
• SystemError: Internal interpreter error.
• SystemExit: Raised by sys.exit().
• TypeError: Invalid operation for type.
• ValueError: Correct type, wrong value.

7. Try and Except Blocks
• Used to catch and handle exceptions gracefully.
• Example:
try:
value = int(input("Enter a number: "))
except ValueError:
print("That's not a valid number!")

8. Else Bock
• Executes if the try block does not raise an exception.
• Example:
try:
result = 10 / 2
except ZeroDivisionError:
print("Cannot divide by zero.")
else:
print("Result is:", result)

9. Finally Block
• Executes regardless of whether an exception occurred or not. Useful for
cleanup actions.
• Example:
try:
file = open("example.txt", "r")
except FileNotFoundError:
print("File not found.")
finally:
file.close() # Ensures the file is closed

10. Raising Exceptions
• You can raise exceptions intentionally using the raise keyword.
• Example:
def check_age(age):
if age < 0:
raise ValueError("Age cannot be negative.")

11. User-defined Exceptions
• Custom exceptions can be created by inheriting from the built-in
Exception class.
• Example:
class CustomError(Exception):
pass
raise CustomError("This is a custom error message.")

12. APPLICATION IN REAL LIFE
• Financial Transactions:
• In banking systems, exceptions are crucial for managing scenarios like
insufficient funds or invalid account numbers. For example, if a user attempts
to withdraw more money than they have, an exception can be raised to
prevent the transaction and notify the user.
• Automated Systems:
• In automated systems like ATMs, error handling is essential. If the machine
runs out of cash or encounters a technical issue, it can raise exceptions to halt
operations and inform the user, ensuring that no erroneous transactions occur.