Why Does Python\'s `range(start, end)` Exclude the `end` Value?

Range(start, end): Why the Exclusion of the End Value?

Python's range(start, end) function is a commonly used utility that generates a sequence of numbers. However, one peculiar aspect of range() is that it excludes the end value. For example, range(1, 11) returns [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], stopping short at 11.

Why is this the case? The answer lies in the broad usage of range() and the common practices in programming.

1. Uniformity in Indexing:

Programmers often prefer zero-based indexing, where the first element of a sequence is referenced as index 0. Using range(0, 10) would return [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], containing exactly 10 elements, aligning with its length (len(range(0, 10))).

2. Looping and Iterating:

Consider a common loop structure:

for i in range(len(li)):
    pass

If range() included the end value, this loop would iterate one past the valid indices of the list li. Programmers might forget to subtract 1 from len(li) when specifying the range, leading to an invalid loop.

3. Consistency with Iterators:

In Python, the range() function serves as an iterator, producing values one at a time. If it included the end value, it would require an additional check or logic to terminate iteration, adding complexity and potential for errors.

Addressing the Need for Inclusion:

If you frequently find yourself requiring the end value to be included, you can create a custom function that extends the functionality of range():

def range1(start, end):
    return range(start, end + 1)

print(range1(1, 10))  # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

By understanding the reasons behind range()'s exclusion of the end value and by utilizing custom functions when necessary, programmers can effectively leverage this versatile tool in their Python code.

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