Efficiently count word frequencies in python

Question

I\'d like to count frequencies of all words in a text file.

>>> countInFile(\'test.txt\')

should return {\'aaa\':1, \'bbb\':

Answer 1

Combining every ones else's views and some of my own :) Here is what I have for you

from collections import Counter
from nltk.tokenize import RegexpTokenizer
from nltk.corpus import stopwords

text='''Note that if you use RegexpTokenizer option, you lose 
natural language features special to word_tokenize 
like splitting apart contractions. You can naively 
split on the regex \w+ without any need for the NLTK.
'''

# tokenize
raw = ' '.join(word_tokenize(text.lower()))

tokenizer = RegexpTokenizer(r'[A-Za-z]{2,}')
words = tokenizer.tokenize(raw)

# remove stopwords
stop_words = set(stopwords.words('english'))
words = [word for word in words if word not in stop_words]

# count word frequency, sort and return just 20
counter = Counter()
counter.update(words)
most_common = counter.most_common(20)
most_common

Output

(All ones)

[('note', 1),
 ('use', 1),
 ('regexptokenizer', 1),
 ('option', 1),
 ('lose', 1),
 ('natural', 1),
 ('language', 1),
 ('features', 1),
 ('special', 1),
 ('word', 1),
 ('tokenize', 1),
 ('like', 1),
 ('splitting', 1),
 ('apart', 1),
 ('contractions', 1),
 ('naively', 1),
 ('split', 1),
 ('regex', 1),
 ('without', 1),
 ('need', 1)]

One can do better than this in terms of efficiency but if you are not worried about it too much, this code is the best.