How to swap noun cardinals in NLTK

Recipe Objective

This recipe explains how to swap noun carinal.

Swapping Noun Cardinal

The func1 function uses a helper function func0 which helps the func1 function to swap any cardinal that occurs after a noun with the noun so that the cardinal occurs immediately before the noun. Cardinals occur before a cardinal's noun and cardinals in a block refer to a number and are tagged as CD. These Swapping noun cardinals are useful to put the cardinal before the noun. If CD is not found at the beginning or all while we are looking for CD tag then we'll return the tag as it is. We'll swap the noun and cardinal as soon as we encounter a CD with a noun preceding it therefore there must be a noun after CD.

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def func0(t):
   def g(word):
     return word[1] == t
   return g

def func1(w, pred, s=0, itr=1):
   length = len(w)
   e = length if itr > 0 else -1

   for j in range(s, e, itr):
     if pred(w[j]):
       return j

   return None

def func2(w):
   i = func1(w, func0('CD'))
   if not i or not w[i-1][1].startswith('NN'):
     return w

   N, NT = w[i-1]
   w[i-1] = w[i]
   w[i] = N, NT
   return w

func2([('an', 'DT'), ('dog', 'NN'), ('20', 'CD')])