FIFO implementation based on Think Complexity(http://www.greenteapress.com/compmod/html/thinkcomplexity005.html#toc27) and http://code.activestate.com/recipes/68436/

fifo.py

class DictFifo(object):

    def __init__(self):
        self.nextin = 0
        self.nextout = 0
        self.data = {}

    def append(self, value):
        self.data[self.nextin] = value
        self.nextin += 1

    def pop(self, n=-1):
        value = self.data.pop(self.nextout)
        self.nextout += 1
        return value

    def __str__(self):
        return str(self.data)

    __repr__ = __str__