input: Write a function to calculate the square root of a user-defined positive number. The function should take one argument, which is the positive number, and return the square root of that number. If the input number is less than or equal to 0, the function should return an error message.
  assert square_root(100)==10.0
  assert square_root(25)==5.0
  assert square_root(4)==2.0
  assert square_root(0)=="Error: Input must be a positive number."
  assert square_root(-1)=="Error: Input must be a positive number."
output: def square_root(number):
      if number <= 0:
          return "Error: Input must be a positive number."
      return number ** 0.5