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

4 votes333 views5 answers
Module 'datetime' has no attribute 'now' django
Python
15 votes337 views3 answers
Save numpy array to csv
Python
25 votes344 views6 answers
Create new python environment
Python
0 vote321 views1 answer
ValueError: invalid PNG header
Python
0 vote324 views1 answer
Pyhton apend to list
Python
0 vote345 views1 answer
Python star sign before list
Python
0 vote352 views1 answer
Pygame kreis definition
Python
0 vote329 views2 answers
How to make SAPI.SpVoice say a variable in python
Python
33 votes298 views4 answers
Sort and reverse list in python
Python
1 vote354 views1 answer
How to print something with tkinter
Python