How to Return a Default Value if a Key Doesn’t Exist in Python?

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To return a default value if a key doesn’t exist in a dictionary in Python, you can use the get() method or the defaultdict class from the collections module.

  1. Using the get() method: The get() method of a dictionary allows you to retrieve the value associated with a key. If the key doesn’t exist, you can specify a default value to be returned instead. Here’s an example:
my_dict = {"key1": "value1", "key2": "value2"}

# Retrieve the value for a key, with a default value if the key doesn't exist
value = my_dict.get("key3", "default_value")

print(value)  # Output: default_value

In this example, the get() method is used to retrieve the value for the key "key3" from the my_dict dictionary. Since "key3" doesn’t exist in the dictionary, the method returns the default value "default_value" instead.

  1. Using defaultdict: The defaultdict class from the collections module provides a convenient way to define a default value for keys that don’t exist in a dictionary. Here’s an example:
from collections import defaultdict

my_dict = defaultdict(lambda: "default_value")
my_dict["key1"] = "value1"
my_dict["key2"] = "value2"

# Retrieve the value for a key, with the default value if the key doesn't exist
value = my_dict["key3"]

print(value)  # Output: default_value

In this example, defaultdict is created with a lambda function that returns the default value "default_value". When you access a key that doesn’t exist in the dictionary (my_dict["key3"]), the lambda function is called, and the default value is returned.

Using get() or defaultdict allows you to handle cases where a key doesn’t exist in a dictionary, providing a default value as a fallback. Choose the approach that best suits your specific needs and coding style.

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