Logical Error

What is a Logical Error?

A logical error, commonly referred to as a “bug”, is one that occurs in Python programming when a code runs without crashing, but produces incorrect or unexpected results. Unlike syntax errors and runtime errors which are immediately detected by Python’s interpreter or during the program execution respectively, logical errors are not identified by the Python interpreter. This makes them particularly difficult to spot and rectify.

A logical error can occur due to incorrect assumptions, invalid logic, improper sequence of program steps, or wrong arithmetic calculations among others. It generally results in an unintended behavior of the program.

Example of a Logical Error

Consider an example where a Python program is expected to compute the average of two numbers.

1def average(a, b):
2    return a + b / 2

In the code above, the expectation is to calculate the average of a and b by adding them together and dividing the result by 2. But due to operator precedence rules in Python (division occurs before addition), the code performs the division first, making the average calculation incorrect.

Fixing the Logical Error

Correcting logical errors requires understanding the problem beset in the program logic and coming up with the right solution to fix it. In the example above, the logical error can be fixed by using parentheses to ensure the addition happens before division.

1def average(a, b):
2    return (a + b) / 2

With the fix, the code now calculates the average correctly.

Be Cautious!

Logical errors can be hard to spot because the code runs without any error messages. To troubleshoot them, it’s recommended to use debug methods like print statements or utilizing debugging tools available in Python development environments.