Added fibonacci.py with fib(n) and main.

fibonacci.py

@@ -0,0 +1,42 @@
+"""fibonacci.py
+
+Utility to compute Fibonacci numbers.
+
+This module provides:
+- fibonacci(n): Return the nth Fibonacci number for n >= 0.
+- A simple __main__ section that prints the first 10 Fibonacci numbers for quick demonstration.
+"""
+
+def fibonacci(n):
+    """Return the nth Fibonacci number.
+
+    The sequence is defined with:
+      fibonacci(0) == 0
+      fibonacci(1) == 1
+      fibonacci(n) == fibonacci(n-1) + fibonacci(n-2) for n >= 2
+
+    Parameters:
+    - n (int): The index of the Fibonacci number to compute. Must be non-negative.
+
+    Returns:
+    - int: The nth Fibonacci number.
+
+    Raises:
+    - TypeError: If n is not an integer.
+    - ValueError: If n is negative.
+    """
+    if not isinstance(n, int):
+        raise TypeError("n must be an integer")
+    if n < 0:
+        raise ValueError("n must be non-negative")
+
+    a, b = 0, 1
+    for _ in range(n):
+        a, b = b, a + b
+    return a
+
+
+if __name__ == "__main__":
+    # Print the first 10 Fibonacci numbers: fibonacci(0) through fibonacci(9)
+    for i in range(10):
+        print(fibonacci(i))