input: Write a function to generate and print the Fibonacci series up to a specified number of terms 'n', where 'n' is given as an input. If 'n' is less than or equal to 0, print a message indicating that the input should be a positive integer.
  assert fibonacci_series(10)=="Fibonacci Series: 0 1 1 2 3 5 8 13 21 34"
  assert fibonacci_series(5)=="Fibonacci Series: 0 1 1 2 3"
  assert fibonacci_series(-1)=="Please enter a positive integer."
  assert fibonacci_series(0)=="Please enter a positive integer."
  assert fibonacci_series(1)=="Fibonacci Series: 0"
output: def fibonacci_series(n):
      if n <= 0:
          return "Please enter a positive integer."
      elif n == 1:
          return "Fibonacci Series: 0"
      else:
          series = [0, 1]
          for i in range(2, n):
              series.append(series[-1] + series[-2])
          return "Fibonacci Series: " + " ".join(map(str, series))