If you have a sequence of items, and want to determine the most frequently occurring items in it, you can use the collections.Counter class.

words = [
  "look", "into", "my", "eyes", "look", "into", "my", "soul", 
  "it's", "not", "uncommon", "to", "see", "my", "mood", 
  "in", "my", "eyes"
]

from collections import Counter

wcount = Counter(words)
wcount.most_common(3)
## [('my', 4), ('look', 2), ('into', 2)]

You can also check how many times a given item appears in the sequence.

wcount["my"]
## 4

You can increment the amount of items manually.

morewords = ["my", "new", "words", "here"]
wcount.update(morewords)
wcount["my"]
## 5

Mathematical operations are also possible.

a = Counter(words)
b = Counter(morewords)
a
## Counter({'my': 4, 'look': 2, 'into': 2, 'eyes': 2, 'soul': 1, "it's": 1, 'not': 1, 'uncommon': 1, 'to': 1, 'see': 1, 'mood': 1, 'in': 1})
b
## Counter({'my': 1, 'new': 1, 'words': 1, 'here': 1})
c = a + b
c
## Counter({'my': 5, 'look': 2, 'into': 2, 'eyes': 2, 'soul': 1, "it's": 1, 'not': 1, 'uncommon': 1, 'to': 1, 'see': 1, 'mood': 1, 'in': 1, 'new': 1, 'words': 1, 'here': 1})
d = a - b
d
## Counter({'my': 3, 'look': 2, 'into': 2, 'eyes': 2, 'soul': 1, "it's": 1, 'not': 1, 'uncommon': 1, 'to': 1, 'see': 1, 'mood': 1, 'in': 1})