Implement Handling for Negative Range (l > r) in Python's range() Function

[Rosuav (Chris Angelico)]

You can do this with an explicit step argument: range(30, 3, -1)

[MegaIng (Cornelius Krupp)]

The behavior is well defined. Changing it would be a breaking change that would break thousands, if not millions, of scripts.

[pf_moore (Paul Moore)]

@code-with-dhruv

Currently, when using Python’s range() function with parameters where the start value is greater than the end value (e.g., range(30, 3)), it doesn’t provide a default behavior or return value.

Yes it does. It returns an empty range. So changing this would be a significant backward incompatibility, and this proposal would break any code that relies on that behaviour.

@code-with-dhruv

• Call range(30, 3) in Python code.
• Note that the return value is currently undefined or not handled.

It’s not “undefined or not handled” at all:

>>> list(range(30, 3))
[]

@code-with-dhruv

After implementing the proposed handling, calling range(30, 3) should return -1.

range returns an iterator. Making it return an integer (-1) in some cases, but an iterator everywhere else, would be extremely difficult to work with. Python doesn’t use “special return values” (like -1) for error situations, it uses exceptions. But to reiterate, a start value higher than the end value isn’t an error situation - it simply defines an empty range.

[Stefan2 (Stefan)]

@pf_moore

range returns an iterator

No, just an iterable.