Range-like generator

Build a lazy range generator with steps and bounds.

generator yield range iteration lazy

Write a generator function `custom_range(start, stop=None, step=1)` that lazily produces numbers similarly to Python's built-in `range`, but with the following semantics:

- If `stop` is `None`, `start` is treated as the stop value and the sequence starts at 0.
- Otherwise, `start` is the inclusive start and `stop` is the exclusive stop.
- `step` must be non-zero. If `step` is positive, the sequence increases from start to less than stop. If `step` is negative, the sequence decreases from start to greater than stop.
- The generator must yield values one by one (do not return a list).
- The sequence may be empty if start/stop do not align with the step direction.

Implement the function so that it can be used in a for loop or with `list()`.

Constraints

- `start`, `stop`, and `step` are integers.
- `step` is never zero.
- The generator only needs to handle typical integer ranges; no overflow concerns.

Example

>>> list(custom_range(5))
[0, 1, 2, 3, 4]
>>> list(custom_range(2, 8, 2))
[2, 4, 6]
>>> list(custom_range(10, 0, -3))
[10, 7, 4, 1]
>>> list(custom_range(3, 3))
[]

8 points ~12 min

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Hints

Set start/stop properly when stop is None.

Think about whether to increment or decrement based on step's sign.

Use a while loop with a condition that depends on step's sign.

Remember to yield inside the loop, not accumulate a list.

Test Results

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