Try/Except vs. If/Else: When to Use Each for Error Handling

Exception Handling: Try/Except vs. If/Else

When faced with potential errors or exceptions in code, programmers often hesitate between using try/except blocks or if/else statements. While this decision may seem trivial, it can significantly impact code design, performance, and readability.

Try/Except vs. If/Else: Preferred Approach

The general consensus, supported by PEP 20, is to prioritize try/except over if/else when:

• It results in performance improvements by preventing unnecessary lookups or calculations.
• It simplifies code by reducing the number of lines and enhancing readability.

Speed Optimization

Consider the example of accessing an element in a list:

<code class="python">try:
    x = my_list[index]
except IndexError:
    x = 'NO_ABC'</code>

Here, try/except is advantageous when the index is likely to be found in the list, minimizing the occurrence of IndexError. In contrast, an if/else approach would necessitate an additional lookup:

<code class="python">if index < len(my_list):
    x = my_list[index]
else:
    x = 'NO_ABC'

Exception Handling and Readability

Python encourages the usage of exceptions as part of its EAFP (Easier to ask for forgiveness than permission) philosophy. By catching errors gracefully in try/except blocks, programmers ensure that exceptions do not silently pass. Additionally, try/except allows for more concise and elegant code:

<code class="python">Worse (LBYL: 'look before you leap'):

if not isinstance(s, str) or not s.isdigit():
    return None
elif len(s) > 10:    #too many digits for int conversion
    return None
else:
    return int(s)

Better (EAFP: Easier to ask for forgiveness than permission):

try:
    return int(s)
except (TypeError, ValueError, OverflowError): #int conversion failed
    return None</code>

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