input: Write a function to generate the first n Fibonacci numbers.
  assert list(fibonacci(5)) == [0, 1, 1, 2, 3]
  assert list(fibonacci(7)) == [0, 1, 1, 2, 3, 5, 8]
  assert list(fibonacci(10)) == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
output: def fibonacci(n):
      fibs = []
      a, b = 0, 1
      for _ in range(n):
          fibs.append(a)
          a, b = b, a + b
      return fibs