Nltk: Porter stemmer returns a capital instead of lowercase

For any stemming, are we not first supposed to convert them into lowercase as part of normalization?

Another example of capitalized output using Oh

>>> from nltk.stem import PorterStemmer
>>> porter = PorterStemmer()
>>> porter.stem('Oh')
'Oh'

I think it's because originally it wants to remain the original form of abbreviations when the word length less than 2, like abbreviations for states.

def stem(self, word):
    stem = word.lower()

    if self.mode == self.NLTK_EXTENSIONS and word in self.pool:
        return self.pool[word]

    if self.mode != self.ORIGINAL_ALGORITHM and len(word) <= 2:
        # With this line, strings of length 1 or 2 don't go through
        # the stemming process, although no mention is made of this
        # in the published algorithm.
        return word

    stem = self._step1a(stem)
    stem = self._step1b(stem)
    stem = self._step1c(stem)
    stem = self._step2(stem)
    stem = self._step3(stem)
    stem = self._step4(stem)
    stem = self._step5a(stem)
    stem = self._step5b(stem)

    return stem

The word 'In' and 'Oh' both are not in self.pool, and len(word)<=2, which means it doesn't satisfy the stem condition here, so it remains the same.

If it's not assigned, may I work on this? Its my first time contributing to a project.

@PhanatosZou feel free to make the changes and create a pull request. The main code that needs to be changed is:

if self.mode != self.ORIGINAL_ALGORITHM and len(word) <= 2:
    # With this line, strings of length 1 or 2 don't go through
    # the stemming process, although no mention is made of this
    # in the published algorithm.
    return stem

But it'll be good to check all keys in self.pool and if they are non-caps, then make changes to this too:

if self.mode == self.NLTK_EXTENSIONS and word in self.pool:
    return self.pool[stem]

Sounds good! I'll work on it.