Why Does Python\'s Slice and Range Functions Exclude the Stop Value?

Why is the Upper Bound of Python's Slice and Range Functions Exclusive?

Python's slice and range functions exclude the stop value from the resulting range or slice. This decision was made for several reasons.

First, it allows for a consistent representation of the elements. The slice operator ([:]) will return all elements in the sequence, the slice operator with a single parameter ([:x]) will return the first x elements, and the slice operator with two parameters ([x:y]) will return the elements from index x (inclusive) to index y (exclusive). This consistency simplifies code readability and reduces the potential for errors.

Additionally, the exclusive stop value allows for easy concatenation of ranges. For example, word[:2] will return the first two characters of a word, and word[2:] will return everything except the first two characters. By combining these two ranges, we can easily retrieve the entire word: word[:2] word[2:] == word.

Furthermore, this design choice aligns with the C programming language's for loop idiom. The typical C for loop is written as for (i = start; i < stop; i ), where start is the starting index, stop is the ending index (exclusive), and i is the loop variable. Python's range function mirrors this syntax, allowing for easier code portability between the two languages.

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