user:
<user_query>
Can you help me create a simple Python function to calculate fibonacci numbers?
</user_query>

assistant:
<think>
The user wants a fibonacci function. I should create a simple, efficient implementation.
I'll use an iterative approach rather than recursive to avoid stack overflow for large numbers.
</think>

I'll create a simple iterative fibonacci function for you.

[Tool call] Write
  path: /Users/test/project/fibonacci.py
  contents: def fibonacci(n: int) -> int:
    if n <= 1:
        return n
    a, b = 0, 1
    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

[Tool result] Write

assistant:
I've created the fibonacci function at `fibonacci.py`. Here's what it does:

- Returns `n` directly for n <= 1 (base cases: fib(0)=0, fib(1)=1)
- Uses iterative approach to avoid recursion limits
- Time complexity: O(n), Space complexity: O(1)

Would you like me to add tests for this function?

user:
<user_query>
Yes, please add some tests
</user_query>

assistant:
<think>
I'll add pytest-style unit tests covering edge cases and normal values.
</think>


[Tool call] Write
  path: /Users/test/project/test_fibonacci.py
  contents: import pytest
from fibonacci import fibonacci

def test_base_cases():
    assert fibonacci(0) == 0
    assert fibonacci(1) == 1

def test_small_values():
    assert fibonacci(2) == 1
    assert fibonacci(5) == 5
    assert fibonacci(10) == 55

[Tool result] Write

assistant:
I've added the test file. You can run the tests with:

```bash
pytest test_fibonacci.py -v
```
