Shadowing a Built-in Function (Part 1, 4: Arithmetic operations)

[mpaunovic]

sum = 0

number = int(input("First number: "))
sum = sum + number

number = int(input("Second number: "))
sum = sum + number

number = int(input("Third number: "))
sum = sum + number

print(f"The sum of the numbers: {sum}")

As you may well be aware, sum is a built-in function in Python (used for adding up items in lists, etc.). While Python allows us to use sum as a variable name, it "shadows" the built-in function, which can lead to confusing bugs later in our code. It is safer to use a name like total_sum instead.

For example, comment out the first line and try to run the code. It should result in a NameError, but it raises a TypeError instead. Why? A NameError only occurs when Python cannot find a name anywhere (not in our local variables, global variables, or built-in functions). Because # sum = 0 was commented out, Python didn't find sum as a variable, but it did find the pre-existing built-in function sum() that comes built into Python. Therefore, it didn't raise a NameError.

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