input: Write a python function to generate the first n Fibonacci numbers.
  assert generate_fibonacci(5) == [0, 1, 1, 2, 3]
  assert generate_fibonacci(7) == [0, 1, 1, 2, 3, 5, 8]
  assert generate_fibonacci(10) == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
output: def generate_fibonacci(n):
      if n <= 0:
          return []
      fib_sequence = [0]
      if n > 1:
          fib_sequence.append(1)
      for i in range(2, n):
          fib_sequence.append(fib_sequence[-1] + fib_sequence[-2])
      return fib_sequence