# computes the average (mean), the median, and the standard deviation of
# a sequence of numbers from a file

from math import sqrt

def readData(source):
  """ source is a reference to opened file,
  numbers in the file should be separated by white space or next line,
  returns the list of values"""

  result = []

  for line in source:
    nums = line.split() # splitting by white space
    for item in nums:
      try:
        result.append(float(item))
      except:
        print("Warning: non-numerical value located, ignored")

  result.sort()

  return result

def getMean(listOfVals):
  """ returns the mean/average of values in the list listOfVals """
  
  return sum(listOfVals)/len(listOfVals)

def getMedian(listOfVals):
  """ returns the middle element of the list listOfVals if odd number of elements,
  and the average of two middle elements if even number of elements """
  
  n =len(listOfVals) 

  if n % 2 == 0:
    return (listOfVals[n//2] + listOfVals[n//2 - 1])/2
  else:
    return listOfVals[n//2]

def getS(vals):
  """ returns the standard deviation of the list of values vals """

  mean = getMean(vals)
  s = 0

  for value in vals:
   s += (mean - value)**2

  return sqrt( s / (len(vals) - 1) )
    

def main():

  fname = input("Enter the file name:")
  source = open(fname)

  listOfValues = readData(source)

  mean = getMean(listOfValues)
  median = getMedian(listOfValues)
  standardDeviation = getS(listOfValues)

  print("Here are the values read from file:")
  for item in listOfValues:
    print(item, end=", ")
  print()

  print("Their mean(average) is ",mean,", ")
  print("their median is ",median,", and")
  print("their standard deviation is ",standardDeviation)

main()