Try vs. If in Python: When Should You Use Each for Variable Evaluation?

Try vs. If in Python: Evaluating Variables for Values

When determining whether a variable has a value, programmers often face the choice between utilizing try/except or if/else constructs. This article explores the rationale behind each approach, based on the principle of EAFP (Easier to Ask for Forgiveness than Permission).

EAFP and Try/Except

EAFP is a coding style that anticipates potential errors and handles them with try/except blocks. This approach assumes the presence of valid values and attempts to operate as normal. If an exception occurs, it is caught and handled accordingly. This method is efficient when exceptions are infrequent.

LBYL and If/Else

In contrast, LBYL (Look Before You Leap) involves checking for conditions before performing operations. Using an if/else block, it verifies if a variable has a value before proceeding. While this approach prevents potential errors, it introduces overhead in situations where the variable is likely to have a value.

Comparison of Efficiency

Empirical measurements show that if/else blocks incur a constant cost, regardless of whether an error occurs or not. On the other hand, try/except blocks have a low setup cost but can be significantly more expensive when exceptions occur. Therefore, choosing the appropriate approach depends on the likelihood of encountering exceptions.

If exceptions are expected to be rare (less than 50%), using try/except is recommended for its efficiency. If exceptions are more frequent, if/else is the better choice to avoid unnecessary performance impacts.

Conclusion

Whether to use try/except or if/else for variable evaluation depends on the expected frequency of exceptions. When exceptions are exceptional, EAFP and try/except provide a faster and more concise solution. However, for more frequent exceptions, LBYL and if/else offer better performance and explicit error handling.

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