Exception Handling Examples

Python Exceptions Python Exceptions are events that occur during the execution of a program that disrupt the normal flow of instructions. They are a way for Python to signal that something unexpected or erroneous has happened. Handling exceptions gracefully is crucial for writing robust and reliable code.

Key Concepts:

try...except block: This is the fundamental construct for handling exceptions.

try:
  # Code that might raise an exception
  result = 10 / 0  
except ZeroDivisionError:
  # Code to handle the specific exception
  print("Error: Division by zero!")
except Exception as e: #Catches any other exception.  Should be used cautiously.
    print(f"An unexpected error occurred: {e}")
else: #Optional block that executes only if no exception occurred.
    print(f"Result: {result}")
finally: #Optional block that ALWAYS executes, regardless of exceptions.  Good for cleanup.
    print("This always runs.")

Types of Exceptions: Python has a rich hierarchy of built-in exceptions. Some common ones include:
- ZeroDivisionError: Division by zero.
- TypeError: Operation on incompatible types.
- ValueError: Incorrect value passed to a function.
- FileNotFoundError: Attempting to open a non-existent file.
- IndexError: Accessing an index outside the bounds of a sequence.
- KeyError: Accessing a non-existent key in a dictionary.
- NameError: Referencing an undefined variable.
Raising Exceptions: You can explicitly raise exceptions using the raise keyword. This is useful for signaling errors in your own functions.

def validate_age(age):
  if age < 0:
    raise ValueError("Age cannot be negative")
  # ... rest of the function ...

Custom Exceptions: You can create your own exception classes by inheriting from the built-in Exception class or its subclasses. This allows you to define specific exception types for your application’s needs. (Custom Exception Classes)
Exception Handling Best Practices:
- Be specific in your except blocks. Catch only the exceptions you expect and know how to handle. Avoid a bare except: clause unless absolutely necessary.
- Use try...except...finally to ensure cleanup actions (like closing files) are always performed.
- Log exceptions for debugging purposes. (Logging in Python)
- Don’t catch exceptions silently unless you have a very good reason (e.g., handling minor issues that the user doesn’t need to see).

Related Notes:

Python Exceptions

Carson West

Exception Handling Examples