input: Write a function to calculate the square root of a given positive number. You can use the math module for this purpose. If the number is negative, return an error message indicating that the number must be positive.
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(25)==5.0
  assert calculate_square_root(0)==0.0
  assert calculate_square_root(-4)=='The number must be positive'
  assert calculate_square_root(64)==8.0
output: def calculate_square_root(number):
      if number < 0:
          return 'The number must be positive'
      return math.sqrt(number)