Title: How To Use Default Dicts
Slug: how_to_use_default_dicts
Summary: How To Use Default Dicts in Python.
Date: 2016-01-23 12:00
Category: Python
Tags: Basics
Authors: Chris Albon

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Preliminaries



In [1]:

    
import collections

Create A DefaultDict

Default Dicts work just like regular dictionaries, except a key is called that doesn't have a value, a default value (note: value, not key) is supplied.



In [2]:

    
# Create a defaultdict with the default value of 0 (int's default value is 0)
arrests = collections.defaultdict(int)

Add A New Key With A Value



In [3]:

    
# Add an entry of a person with 10 arrests
arrests['Sarah Miller'] = 10



In [4]:

    
# View dictionary
arrests









    Out[4]:





defaultdict(int, {'Sarah Miller': 10})

Add A New Key Without A Value



In [5]:

    
# Add an entry of a person with no value for arrests,
# thus the default value is used
arrests['Bill James']









    Out[5]:





0



In [6]:

    
# View dictionary
arrests









    Out[6]:





defaultdict(int, {'Bill James': 0, 'Sarah Miller': 10})