Defaultdict is a subclass of built-in dict class that returns dictionary-like object. It is present in Collections module.
Functionality
Both dict and defaultdict have similar functionalities except that in defaultdict a default value is provided for the key that does not exist.
Note: For more information, please check Python Dictionaries .
Creating Defaultdict
Default dict can be created using built-in defalutdict( ) function:
# importing defaultdict from the collections module
from collections
import defaultdict
def default_factory( ):
return "Deafult Value"
defDict = defaultdict( default_factory )
defDict["alpha"] = 0
defDict["beta"] = 1
print(defDict["gamma"])
print(defDict["alpha"])
default_factory: An attribute which is a function
returning the default value for the dictionary defined. If this argument is
absent then the dictionary raises a KeyError.
If default_factory attribute is absent: KeyError is raised
Using int as default_factory
When the int class is used as a default_factory and passed to the defaultdict( ), zero is used as default value for the key that does not exists.
defDict = defaultdict( int )
defDict["alpha"] = 1
defDict["beta"] = 2
print(defDict["alpha"])
