Fibonacci Sequence Generator

def fibonacci():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a + b

def fibonacci_nth(n):
    """Get the nth Fibonacci number (0-indexed)"""
    if n <= 1:
        return n
    
    a, b = 0, 1
    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

def fibonacci_range(start, end):
    """Generate Fibonacci numbers in a range"""
    gen = fibonacci()
    result = []
    for num in gen:
        if num > end:
            break
        if num >= start:
            result.append(num)
    return result