How to set default value to all keys of a dict object in python?

Question

I know you can use setdefault(key, value) to set default value for a given key, but is there a way to set default values of all keys to some value after creating a dict ?

Put it another way, I want the dict to return the specified default value for every key I didn't yet set.

Answer 1

You can replace your old dictionary with a defaultdict:

>>> from collections import defaultdict >>> d = {'foo': 123, 'bar': 456} >>> d['baz'] Traceback (most recent call last):   File "<stdin>", line 1, in <module> KeyError: 'baz' >>> d = defaultdict(lambda: -1, d) >>> d['baz'] -1 

The "trick" here is that a defaultdict can be initialized with another dict. This means that you preserve the existing values in your normal dict:

>>> d['foo'] 123 

Answer 2

Use defaultdict

from collections import defaultdict a = {}  a = defaultdict(lambda:0,a) a["anything"] # => 0 

This is very useful for case like this,where default values for every key is set as 0:

results ={ 'pre-access' : {'count': 4, 'pass_count': 2},'no-access' : {'count': 55, 'pass_count': 19} for k,v in results.iteritems():   a['count'] += v['count']   a['pass_count'] += v['pass_count']