CODEWITHSUNDEEP
python
Rahul Deshmukh
Rahul Deshmukh

Reputation: 88

why doesn't this Python dictionary comprehension work for counting words in an input()?

I have to count the how many times a word is used in a sentence. I have found the solution, however i want the code to be more concise and want to solve it using dictionary comprehension. Can someone please help me understand what is wrong with the following code?

user_input = input().lower().split()
usage_dict = dict()
usage_dict = {word:usage_dict.get(word, 0) + 1 for word in user_input}
print(usage_dict)

Input : a aa abC aa ac abc bcd a

Output : {'a': 1, 'aa': 1, 'abc': 1, 'ac': 1, 'bcd': 1}

Expected Output: {'a': 2, 'aa': 2, 'abc': 2, 'ac': 1, 'bcd': 1}

Upvotes: 0

Views: 105

Answers (4)

azro
azro

Reputation: 54168

Problem

The usage_dict dictionnary is created once the dict-comprehension is ended, there is no concept of temporary state of the dict, so usage_dict.get(word, 0) always gives 0

That is working only in a for loop:

usage_dict = {}
for word in user_input:
    usage_dict[word] = usage_dict.get(word, 0) + 1

Solutions

Use list.count()

usage_dict = {word: user_input.count(word) for word in set(user_input)}

Use collections.Counter which uses the same for loop that above

usage_dict = Counter(user_input)

Upvotes: 3

U13-Forward
U13-Forward

Reputation: 71600

You could use a dictionary comprehension:

user_input = input().lower().split()
usage_dict = {word: user_input.count(word) for word in user_input}
print(usage_dict)

Or use collections.Counter:

import collections
user_input = input().lower().split()
usage_dict = collections.Counter(user_input)
print(usage_dict)

Both codes output:

{'a': 2, 'aa': 2, 'abc': 2, 'ac': 1, 'bcd': 1}

The reason it doesn't work is because getting the count of value in the middle of a dictionary comprehension doesn't work, because it has to first finish the dictionary comprehension then assign it as a variable named usage_dict.

Upvotes: 0

balderman
balderman

Reputation: 23815

Use Counter. See below

from collections import Counter

data = 'a aa abC aa ac abc bcd a'.split()
c = Counter(data)
print(c)

output

Counter({'a': 2, 'aa': 2, 'abC': 1, 'ac': 1, 'abc': 1, 'bcd': 1})

Upvotes: 0

user15801675
user15801675

Reputation:

Try to use Counter

from collections import Counter

user_input = input().lower().split()
usage_dict = Counter(user_input)
print(usage_dict)

Or:

usage_dict = {x:user_input.count(x) for x in user_input}

Returns

{'a': 2, 'aa': 2, 'abc': 2, 'ac': 1, 'bcd': 1}

Upvotes: 0

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