When to Use 'try' vs. 'if' for Handling Potential None Values in Python?

When to Use 'try' vs. 'if' for Value Testing in Python

In Python, when testing if a variable has a value, the choice between using 'try' or 'if' often arises. This question aims to provide guidance on the rationale behind each construct.

Consider a function that returns either a list or no value. To check the result before processing, we have two options:

result = function();
if (result):
    for r in result:
        # process items

or

result = function();
try:
    for r in result:
        # Process items
except TypeError:
    pass;

Rationale for 'try'/'except'

The 'try'/'except' approach assumes the presence of a value within 'result' and handles potential exceptions (e.g., TypeError if the function returns None). This follows the EAFP (Easier to Ask for Forgiveness than Permission) principle, which favors catching exceptions when they occur rather than checking for them beforehand. It is more efficient in scenarios where exceptions are uncommon.

Rationale for 'if'

The 'if' approach explicitly checks for the presence of a value before attempting to process it. While it can be slower, it is recommended when exceptions are expected to occur frequently (i.e., when 'result' is likely to be None in this case).

Conclusion

The choice depends on the expected frequency of exceptions. For infrequent exceptions, 'try'/'except' is faster and follows the EAFP principle. Otherwise, 'if' is more prudent to avoid unnecessary exception handling.

Additional Considerations

• The Python documentation recommends using 'try'/'except' for flow control when exceptions are exceptional.
• 'if' statements always incur a cost, while 'try'/'except' setup is nearly free, but handling exceptions is more expensive.
• The EAFP style is considered "pythonic" and encourages clean and concise code.

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