Comments on: FIFO Data Structure in Python

By: ade

ade — Mon, 01 May 2006 10:27:25 +0000

Thanks I hadn’t realised that. Come to think of it the list class has a pop method I could have used.

Anyway if you’re interested in a highly-performant Fifo class then take a look at the bottom of this Python Cookbook entry: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/68436

By: Daniel Lemire

Daniel Lemire — Mon, 01 May 2006 00:49:48 +0000

Because the expected popping time of your solution is linear with respect to the size of the list. Specifically, doing “del self.items[0]” can be tremendously expensive since Python needs to copy the entire array to a new location in memory. Doing so thousands of times is highly inefficient.

By: ade

ade — Sun, 30 Apr 2006 22:16:55 +0000

Why not try something simpler like this:

class Fifo:
def __init__(self):
self.items = []

def append(self, item):
self.items.append(item)

def pop(self):
item = self.items[0]
del self.items[0]
return item

def __len__(self):
return len(self.items)

def tolist(self):
#defensive copy
return self.items[:]

import unittest
class FifoTest(unittest.TestCase):
def testItemsArePoppedInSameOrderTheyWereRemoved(self):
fifo = Fifo()
fifo.append(‘a’)
fifo.append(‘b’)
fifo.append(‘c’)
self.assertEquals(‘a’, fifo.pop())
self.assertEquals(‘b’, fifo.pop())
self.assertEquals(‘c’, fifo.pop())

def testFifoLengthChangesAsItemsAreRemoved(self):
fifo = Fifo()
fifo.append(‘a’)
fifo.append(‘b’)
fifo.append(‘c’)
self.assertEquals(3, len(fifo))
fifo.pop()
self.assertEquals(2, len(fifo))
fifo.pop()
self.assertEquals(1, len(fifo))
fifo.pop()
self.assertEquals(0, len(fifo))

def testFifoCanBeConvertedToList(self):
fifo = Fifo()
fifo.append(‘a’)
fifo.append(‘b’)
fifo.append(‘c’)
self.assertEquals(['a','b','c'], fifo.tolist())
if __name__ == ‘__main__’:
suite = unittest.TestSuite()
suite.addTest(unittest.makeSuite(FifoTest))
unittest.TextTestRunner(verbosity=3).run(suite)