Cookbooks
Python
Chapter 5. Good Coding Practices
Handling errors

Python:
Handling errors

How to: 

# Basic try-except block
try:
    # risky code
    number = int(input("Enter a number: "))
except ValueError:
    # handle error
    print("That's not a number!")

# Specifying multiple exceptions
try:
    # code that might raise different exceptions
    result = 10 / int(input("Enter a divisor: "))
except ZeroDivisionError:
    print("Oops! Can't divide by zero.")
except ValueError:
    print("I need a number, buddy.")

# Using else and finally
try:
    number = int(input("Enter a number for squaring: "))
except ValueError:
    print("I said a number!")
else:
    # no errors occurred
    print("Your number squared is:", number**2)
finally:
    # always executes
    print("Thanks for trying this out!")

Sample output when entering an invalid number for the first block:

Enter a number: hello
That's not a number!

Deep Dive

Since the dawn of programming, error handling has been crucial. Early approaches were rudimentary, like checking conditions before every risky operation. Python’s try-except syntax came from a heritage of exception handling in older languages like C++ and Java, simplifying the process.

When you try a block of code, Python watches for any exceptions. If an error pops up, the except block catches it. You can get specific about the exceptions you catch or catch ‘em all with a bare except. However, specifics first is the better approach – it’s precise, not a catch-all net.

else and finally are extras in this concept. The else block runs if the try block is error-free. finally is the reliable buddy that runs no matter what – think cleanup operations.

Alternatives? There sure are. Some languages use return codes instead of exceptions. You might also encounter with statements for handling resources or assertions that check conditions while developing. But when we talk about solid error-handling strategies, the try-catch model stands out for its readability and structure.

See Also

Here are some good additional resources for diving even deeper:

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