input: Write a function to print out the Fibonacci series up to n numbers where n is a user input. Return the series as a list.
  def fibonacci_series(n):
      if n <= 0:
          return []
      series = [0]
      a, b = 0, 1
      for _ in range(1, n):
          series.append(b)
          a, b = b, a + b
      return series
  
  assert fibonacci_series(10)==[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
  assert fibonacci_series(5)==[0, 1, 1, 2, 3]
  assert fibonacci_series(1)==[0]
  assert fibonacci_series(0)==[]
output: def fibonacci_series(n):
      if n <= 0:
          return []
      series = [0]
      a, b = 0, 1
      for _ in range(1, n):
          series.append(b)
          a, b = b, a + b
      return series