input: Write a function to calculate the square root of a given positive number using Python's math library. If the number is not positive, return a message prompting the user to enter a positive number.
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(25)==5.0
  assert calculate_square_root(0)=="Please enter a positive number."
  assert calculate_square_root(-10)=="Please enter a positive number."
output: import math
  
  def calculate_square_root(number):
      if number > 0:
          return math.sqrt(number)
      else:
          return "Please enter a positive number."