Using "try" vs. "if" to Test Variable Value in Python

In Python, there are situations where you may need to check if a variable has a value before processing it. This dilemma arises when deciding between using "if" or "try" constructs.

"if" Constructs

The "if" statement checks if a condition is True and executes the indented block of code if it is. In your example, using an "if" construct would look like this:

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

This approach assumes that the result variable holds a non-empty value. If result is an empty list or None, an IndexError or TypeError will be raised when trying to iterate over result.

"try" Constructs

A "try" block attempts to execute a block of code and catches any exceptions that may occur. In this case, you can use a try/except block to handle exceptions gracefully:

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

This code will attempt to iterate over the result variable. If it encounters a TypeError due to an empty list or None, it will skip the error and continue execution.

Choosing Between "if" and "try"

The choice between using "if" and "try" depends on the specific situation and the likelihood of an exception being raised.

• Use "if" constructs when:

  • You have a strong expectation that the variable will have a non-empty value.
  • Performance is critical, as "if" checks are faster than "try" blocks.

• Use "try" constructs when:

  • You expect the variable to be empty or null in some cases.
  • You want to handle exceptions gracefully without interrupting the program flow.
• EAFP Style

Python encourages the "EAFP" (Easier to Ask for Forgiveness Than Permission) style, where exceptions are handled after attempting operations that may fail. This approach can be more efficient and concise, as seen in the "try" example above.