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Exception Handling

Python uses try, except, else, and finally blocks to handle exceptions.

try:
    # Code that might raise an exception
    result = 10 / 0
except ZeroDivisionError:
    # Handle the specific exception
    print("Error: Division by zero")
except Exception as e: # Catches any other exception
    print(f"An error occurred: {e}")
else:
    # Code to execute if no exception occurs
    print("Division successful:", result)
finally:
    # Code that always executes, regardless of exceptions
    print("This always runs")

Custom Exceptions (Exception Handling Examples)

Common Exceptions:

ZeroDivisionError: Division by zero.
TypeError: Operation on incompatible types.
NameError: Using an undefined variable.
IndexError: Accessing a list index out of range.
KeyError: Accessing a dictionary key that doesn’t exist.
FileNotFoundError: Trying to open a non-existent file.
IOError: General input/output error.

Raising Exceptions:

You can raise exceptions using the raise keyword:

def my_function(x):
    if x < 0:
        raise ValueError("Input must be non-negative")
    return x * 2

Exception Chaining:

You can chain exceptions to provide more context when an exception is caught and re-raised.

try:
    # some code that may raise an exception
    raise ValueError("Something went wrong")
except ValueError as e:
    raise RuntimeError("A ValueError occurred") from e

File IO Modes Handling Binary Files

Exception Handling

Carson West

Python 1 Home

Exception Handling