How to create a list of values in a dictionary comprehension in Python

Question

Taking a very simple example of looping over a sentence and creating a dictionary which maps {x:y}, where x is a key representing the length of the wor

Answer 1

Sure, you can, using sorted + groupby, but it doesn't look great.

from itertools import groupby
d = dict([(k, list(g)) for k, g in groupby(sorted(mywords.split(), key=len), key=len)])

print(d)
{2: ['be', 'be'],
 3: ['May', 'and'],
 4: ['your', 'your'],
 5: ['short'],
 6: ['coffee', 'strong', 'Monday']}

_{P.S., Here's my answer (using defaultdict that I recommend over this) to the original question.}

Answer 2

Don't try to cram everything in one line, it won't be readable. This is a simple, easy-to-understand solution, even if it takes a couple of lines:

from collections import defaultdict

mywords = "May your coffee be strong and your Monday be short"    
ans = defaultdict(list)

for word in mywords.split():
    ans[len(word)].append(word)