input: Write a function to calculate the square root of a user-defined positive number. Use the math library to calculate the square root. If the number is negative, print an error message. The function should accept one parameter, which is the number for which you want to find the square root.
  
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(25)==5.0
  assert calculate_square_root(16)==4.0
  assert calculate_square_root(-16)=="Error: Number must be positive."
output: import math
  
  def calculate_square_root(number):
      if number < 0:
          return "Error: Number must be positive."
      return math.sqrt(number)