Understanding the 'else' Clause in Python's 'try' Statement

Python's exception handling mechanism provides three optional clauses— except, else, and finally — that can be used with the try clause. Each has a specific purpose and they together offer a robust way to anticipate and manage errors or exceptions in your code. This article focuses on the else clause, which many programmers find a bit tricky to use or understand.

The else clause in a try statement in Python executes if and only if the try block does not raise an exception. This makes it different from the other two clauses.

Consider the following example:

try:
    # attempt this code block
    num = int(input("Enter a integer: "))
except ValueError:
    # handle exception
    print("That's not an integer!")
else:
    # executes if the try block does not raise an exception
    print("The square of the number is", num**2)

In this example, when you enter a string instead of an integer, a ValueError exception is raised, and the except block is executed. However, if you enter an integer, no exception is raised, the try block successfully completes, and the else block is executed, printing the square of the entered number.

Contrary to some misconceptions, the else block is not an alternative to the finally block. While the else clause runs when no exceptions occur, the finally clause always runs, regardless of whether an exception was raised or not.

A best practice when coding in Python is to make use of these exception handling clauses to create resilient programs. The else clause in a try block can be particularly handy when there is a certain action that must only take place when no exceptions occur in the try block, but should not be performed if an exception does occur.

In essence, the else block helps you segregate the normal flow of your program (the try block) from your error handling (the except block), and from actions contingent upon the success of the try block (the else block). This leads to cleaner, more maintainable code.