Python Filter/ compare every second value in a sequence [duplicate]

This question already has answers here: Closed 11 years ago.

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How to make a function that counts how many times each element is equal to 2 elements to its right

I need help with the prompt below. For some reason I keep on getting a "'int' object is not subscriptable" errpr and don't really know how to fix it. I have a feeling that it has something to do with my helper function.

Here are the Tests:

         '''
             skip(X) counts how many times an item in 
             sequence X is equal to the item 
             "two places to the right" in X.

         Examples:

             skip("evening") is 2, once
                         for 'e' and once for 'n'   
             skipt([1,2,3,4]) is 0 
             skipt([0,0,0,0,0]) is 3, because
                         there are five 0's, but 
                         the last two can't be 
                         compared to item two places
                         to the right. 

>>> X = "onoratitatio" 
>>> skip(X)
3
>>> Y = 2*[3,1]+4*[1,5] 
>>> skip(Y)
8
>>> skip([5])
0
'''

Here is what I have currently created:

def helper(X):
    return X[0] == X[2]

def skip(X):
    return len(filter(helper,X))

I don't really know, but I'm about fed up w开发者_运维技巧ith this problem. Does anyone have any ideas?

---

In [4]: word = "mississippi"    
In [5]: word_list = [w for w in xrange(len(word) - 2) if word[w] == word[w + 2]]
In [6]: print len(word_list)
1

In [7]: word = "evening"
In [8]: word_list = [w for w in xrange(len(word) - 2) if word[w] == word[w + 2]]
In [9]: print len(word_list)
2

---

You can't do this with filter(), because filter takes a single value from an iterable and has no way to know the whole iterable you are trying to test.

What @chown is trying to tell you is that you can fix skip() by using the same answer your classmate got...

def skip(X):
    return len([w for w in xrange(len(X) - 2) if X[w] == X[w + 2]])

Explicitly...

>>> def skip(X):
...     return len([w for w in xrange(len(X) - 2) if X[w] == X[w + 2]])
... 
>>> skip('evening')
2
>>> skip([1,2,3,4])
0
>>> skip([0,0,0,0,0])
3
>>> skip("onoratitatio")
3
>>>