How to use int as default_factory In Python
When the int class is passed as the default_factory argument, then a defaultdict is created with default value as zero.
Example:
Python3
# Python program to demonstrate # defaultdict from collections import defaultdict # Defining the dict d = defaultdict(int) L = [1, 2, 3, 4, 2, 4, 1, 2] # Iterate through the list # for keeping the count for i in L: # The default value is 0 # so there is no need to # enter the key first d[i] += 1 print(d) |
Output:
defaultdict(<class 'int'>, {1: 2, 2: 3, 3: 1, 4: 2})
Defaultdict in Python
Dictionary in Python is an unordered collection of data values that are used to store data values like a map. Unlike other Data Types that hold only single value as an element, the Dictionary holds key-value pair. In Dictionary, the key must be unique and immutable. This means that a Python Tuple can be a key whereas a Python List can not. A Dictionary can be created by placing a sequence of elements within curly {} braces, separated by ‘comma’.
Example:
Python3
# Python program to demonstrate # dictionary Dict = {1: 'Geeks', 2: 'For', 3: 'Geeks'} print("Dictionary:") print(Dict) print(Dict[1]) # Uncommenting this print(Dict[4]) # will raise a KeyError as the # 4 is not present in the dictionary |
Output:
Dictionary:
{1: 'Geeks', 2: 'For', 3: 'Geeks'}
Geeks
Traceback (most recent call last):
File "/home/1ca83108cc81344dc7137900693ced08.py", line 11, in
print(Dict[4])
KeyError: 4
Sometimes, when the KeyError is raised, it might become a problem. To overcome this Python introduces another dictionary like container known as Defaultdict which is present inside the collections module.
Note: For more information, refer to Python Dictionary.