Why Does Python Use Exclusive Upper Bounds in Slices and Ranges?

Python's Exclusive Upper Bound in Slices and Ranges

Python's slice and range features employ an exclusive upper bound, meaning the stop value is not included in the resulting sequence. This design decision arises from several factors.

Concise Notation and Predictability:

• Exclusive upper bounds allow for concise expressions by aligning the range with the start value. For instance, range(0, x) produces a range with x elements, maintaining consistency.

Compatibility with C Syntax:

• Python's for loop syntax resembles C's for loop idiom, which uses exclusive upper bounds to iterate over arrays. This ensures easy code portability between the two languages.

String Manipulation Invariants:

• It supports useful string manipulation patterns. For instance:

  • word[:2] retrieves the first two characters.
  • word[2:] omits the first two characters.
  • word[:i] word[i:] equals the original word, ensuring completeness.

Range Consistency:

• The range function operates similarly to slices for consistency, offering developers a uniform syntax for defining sequences.
• The difference between the indices in a valid non-negative range defines its length.

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