input: def mean_median(arr): 
      """
      Calculate and return the mean and median of a given array of numbers.
  
      >>> mean_median([10, 15, 20, 25, 30, 35])
      (22.5, 22.5)
      """
      
      arr_sum = 0 
      for i in range(len(arr)): 
          arr_sum += arr[i] 
      
      mean = arr_sum/len(arr) 
      
      arr = sorted(arr) 
      if len(arr) % 2 != 0: 
          median = arr[len(arr)//2] 
      else: 
          median = (arr[len(arr)//2] + arr[len(arr)//2 - 1]) / 2
      
      return mean, median
output:     arr_sum = 0 
      for i in range(len(arr)): 
          arr_sum += arr[i] 
      
      mean = arr_sum/len(arr) 
      
      arr = sorted(arr) 
      if len(arr) % 2 != 0: 
          median = arr[len(arr)//2] 
      else: 
          median = (arr[len(arr)//2] + arr[len(arr)//2 - 1]) / 2
      
      return mean, median