input: Write a python function to generate a Fibonacci sequence of length n.
  assert fibonacci(1) == [1]
  assert fibonacci(2) == [1, 1]
  assert fibonacci(5) == [1, 1, 2, 3, 5]
  assert fibonacci(7) == [1, 1, 2, 3, 5, 8, 13]
output: def fibonacci(n):
      if n <= 0:
          return []
      elif n == 1:
          return [1]
      fib_seq = [1, 1]
      while len(fib_seq) < n:
          fib_seq.append(fib_seq[-1] + fib_seq[-2])
      return fib_seq