algs=['fifo', 'lru', 'liu']
refstring=[3,4,6,8,7,5,1,3,1,5,6,0,4,5,2,7,4,3,2,7,0,3,3,6,3]
framesizes=[3,4,5] # number of frames to test against algorithm
algpgm={}
...

for alg in algs:
  execfile(alg+'.py')        # define the replacement class
  algpgm[alg]=eval(alg+'()') # instantiate the class
  ...
  for numframes in framesizes: # test algorithm on this many frames
    ...
    for p in refstring:
      ...algpgm[alg].ref(p,w) # invoke the ref method dynamically
    ...
  ...