COLLECTIONS.DEFAULTDICT(set)

From collections import defaultdict

>>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
>>> d = defaultdict(list)
>>> for k, v in s:
...     d[k].append(v)
...
>>> d.items()
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

Source: docs.python.org

COLLECTIONS.DEFAULTDICT(set)

defaultdict means that if a key is not found in the dictionary,
then instead of a KeyError being thrown, a new entry is created. 
The type of this new entry is given by the argument of defaultdict.

For example:

somedict = {}
print(somedict[3]) # KeyError

someddict = defaultdict(int)
print(someddict[3]) # print int(), thus 0

>>> from collections import defaultdict

Similar codes

41 votes235 views6 answers
How to flatten list of lists in python
Python
0 vote273 views1 answer
How to sort dataframe in python by length of groups
Python
21 votes270 views3 answers
Display text in pygame
Python
0 vote266 views1 answer
Get UTC time for IST time python
Python
0 vote277 views1 answer
DataFrame.plot.line() method: | dataframe line plot
Python
-1 vote246 views1 answer
How to play mp3 file form pygame module
Python
0 vote267 views1 answer
Add a title to pandas dataframe
Python
3 votes291 views2 answers
Multiple Regression in Python
Python
0 vote271 views1 answer
ImportError: cannot import name 'StringIO'
Python
0 vote234 views1 answer
Cv2 open blank window
Python