遍历Python中4个函数的不同排列

Question

OK I am using different taggers to tag a text. Default, unigram, bigram and trigram.

I have to check which combination of three of those four taggers is the most accurate.

To do that i have to loop through all the possible combinations which i do like this:

permutaties = list(itertools.permutations(['default_tagger','unigram_tagger',
                                              'bigram_tagger','trigram_tagger'],3))
resultaten = [] 
for element in permutaties:
        resultaten.append(accuracy(element))

so each element is a tuple of three tagmethods like for example: ('default_tagger', 'bigram_tagger', 'trigram_tagger')

In the accuracy function I now have to dynamically call the three accompanying methods of each tagger, the problem is: I don't know how to do this.

The tagger functions are as follows:

unigram_tagger = nltk.UnigramTagger(brown_train, backoff=backofff)

bigram_tagger = nltk.BigramTagger(brown_train, backoff=backofff)

trigram_tagger = nltk.TrigramTagger(brown_train, backoff=backofff)

default_tagger = nltk.DefaultTagger('NN')

So for the example the code should become:

t0 = nltk.DefaultTagger('NN')
t1 = nltk.BigramTagger(brown_train, backoff=t0)
t2 = nltk.TrigramTagger(brown_train, backoff=t1)
t2.evaluate(brown_test)

So in essence the problem is how to iterate through all 24 combinations of that list of 4 functions.

Any Python Masters that can help me?

Answer 1

Not shure if I understood what you need, but you can use the methods you want to call themselves instead of strings - sou your code could become soemthing like:

permutaties = itertools.permutations([nltk.UnigramTagger, nltk.BigramTagger, nltk.TrigramTagger, nltk.DefaultTagger],3)
resultaten = [] 
for element in permutaties:
     resultaten.append(accuracy(element, brown_Train, brown_element))

def accuracy(element, brown_train,brown_element):
     if element is nltk.DeafultTagger:
        evaluator = element("NN")
     else:
        evaluator = element(brown_train, backoff=XXX)  #maybe insert more elif
                    #clauses to retrieve the proper backoff parameter --or you could
                    # usr a tuple in the call to permutations so the apropriate backoff 
                    #is avaliable for each function to be called
     return  evaluator.evaluate(brown_test) # ? I am not shure  from your code if this is your intent

Answer 2

Starting with jsbueno's code, I suggest writing a wrapper function for each of the taggers to give them the same signature. And since you only need them once, I suggest using a lambda.

permutaties = itertools.permutations([lambda: ntlk.DefaultTagger("NN"),
                                      lambda: nltk.UnigramTagger(brown_train, backoff),
                                      lambda: nltk.BigramTagger(brown_train, backoff),
                                      lambda: nltk.TrigramTagger(brown_train, backoff)],3)

This would allow you to call each directly, without a special function that figures out which function you're calling and employs the appropriate signature.

Answer 3

basing on jsbueno code I think that you want to reuse evaluator as the backoff argument so the code should be

permutaties = itertools.permutations([nltk.UnigramTagger, nltk.BigramTagger, nltk.TrigramTagger, nltk.DefaultTagger],3)
resultaten = [] 
for element in permutaties:
     resultaten.append(accuracy(element, brown_Train, brown_element))

def accuracy(element, brown_train,brown_element):
     evaluator = "NN"
     for e in element:
         if evaluator == "NN":
              evaluator = e("NN")
         else:

              evaluator = e(brown_train, backoff=evaluator)  #maybe insert more elif
                    #clauses to retrieve the proper backoff parameter --or you could
                    # usr a tuple in the call to permutations so the apropriate backoff 
                    #is avaliable for each function to be called

     return  evaluator.evaluate(brown_test) # ? I am not shure  from your code if this is your intent