What are some examples of using defaultdict in Python?

What are some examples of using defaultdict in Python?

The defaultdict is a subclass of the built-in dict class. It overrides one method to provide a default value for a nonexistent key. For example, you can use it to count occurrences of items in a list.

Can you show me a code example?

Sure! Here's a simple example:

from collections import defaultdict

# Create a defaultdict with int as the default factory
count = defaultdict(int)

# Count occurrences of each item
for item in ['apple', 'banana', 'apple', 'orange', 'banana', 'banana']:
    count[item] += 1

print(count)

This will output: defaultdict(<class 'int'>, {'apple': 2, 'banana': 3, 'orange': 1}).

What if I want to use a list as the default value?

You can do that by using list as the default factory. Here's an example:

from collections import defaultdict

# Create a defaultdict with list as the default factory
list_dict = defaultdict(list)

# Append items to the list for each key
list_dict['fruits'].append('apple')
list_dict['fruits'].append('banana')
list_dict['vegetables'].append('carrot')

print(list_dict)

This will output: defaultdict(<class 'list'>, {'fruits': ['apple', 'banana'], 'vegetables': ['carrot']}).