import sys

class Stats:

    def __init__(self, sequence):

        # sequence of numbers we will process

        # convert all items to floats for numerical processing

        self.sequence = [float(item) for item in sequence]

    def sum(self):

        if len(self.sequence) < 1:

            return None

        else:

            return sum(self.sequence)

    def count(self):

        return len(self.sequence)

    def min(self):

        if len(self.sequence) < 1:

            return None

        else:

            return min(self.sequence)

    def max(self):

        if len(self.sequence) < 1:

            return None

        else:

            return max(self.sequence)

    def avg(self):

        if len(self.sequence) < 1:

            return None

        else:

            return sum(self.sequence) / len(self.sequence)    

    def median(self):

        if len(self.sequence) < 1:

            return None

        else:

            self.sequence.sort()

            return self.sequence[len(self.sequence) // 2]

    def stdev(self):

        if len(self.sequence) < 1:

            return None

        else:

            avg = self.avg()

            sdsq = sum([(i - avg) ** 2 for i in self.sequence])

            stdev = (sdsq / (len(self.sequence) - 1)) ** .5

            return stdev

    def percentile(self, percentile):

        if len(self.sequence) < 1:

            value = None

        elif (percentile >= 100):

            sys.stderr.write('ERROR: percentile must be < 100.  you supplied: %s\n'% percentile)

            value = None

        else:

            element_idx = int(len(self.sequence) * (percentile / 100.0))

            self.sequence.sort()

            value = self.sequence[element_idx]

        return value