Buckets items by timestamp and counts the items in each bucket

buckets.py

class Buckets(object):
    """
    Buckets items by timestamp and counts the items in each bucket.
    """
    
    def __init__(self, since, interval=300):
        """
        :param since:     Starting timestamp in seconds.
        :type  since:     int
        :param interval:  The bucket size in seconds.
        :type  interval:  int
        """
        
        self.ranges = []
        self.map = {}
        self.since = since
        self.now = int(time.time())
        self.interval = 300
        
        # initialize buckets 
        current = since + interval
        while current < self.now:
            self.ranges.append(current)
            current += interval
        
        # the first bucket
        self.map[str(since) + '-' + str(self.ranges[0])] = 0
        
        # the last bucket
        self.map[str(self.ranges[-1]) + '-' + str(self.now)] = 0
        
        # the rest of the buckets
        for i in range(1, len(self.ranges)):
            prev = i - 1
            self.map[str(self.ranges[prev]) + '-' + str(self.ranges[i])] = 0
        
        self.sortedMap = sorted(self.map)
            
        
    def add(self, timestamp):
        """
        Add another item to the buckets. The ``time`` parameter is used to
        determine which bucket to place the item into.
        
        :param timestamp:  Item timestamp
        :type  timestamp:  int
        """
        
        # determine which bucket to place the item in
        bucket = None
        for i in range(len(self.ranges)):
            if timestamp < self.ranges[i]:
                bucket = self.sortedMap[i]
                break
        
        # we're not smaller than any range - should go in the last bucket
        if bucket is None:
            bucket = self.sortedMap[-1]
        
        self.map[bucket] += 1
    
    def distribution(self):
        return self.map