How To Find A Key In Nested Dictionary Python

In this tutorial, we will learn how to find a key in a nested dictionary in Python. We often use nested dictionaries when working with complex data, and locating a specific key can turn into a daunting task. To solve this issue, we will create a function that will recursively search for the key within nested dictionaries and return the value if it exists.

Step 1: Define a recursive function to find the key

First, let’s define a function find_key() that will take two parameters: the nested dictionary (nested_dict) and the key we are searching for (target_key). If the key exists in the nested dictionary, the function returns the value. If not, it will recursively search inside inner dictionaries.

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def find_key(nested_dict, target_key):
    for key, value in nested_dict.items():
        if key == target_key:
            return value
        if isinstance(value, dict):
            result = find_key(value, target_key)
            if result is not None:
                return result

The find_key() function iterates through key-value pairs of the nested dictionary. If the key matches the target_key, it returns the value, else it continues to search recursively within inner dictionaries.

Step 2: Test the function with an example

Now, let’s test the find_key() function using a nested dictionary. Below is an example nested dictionary.

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example_dict = {
    "A": {
        "B": {
            "C": {
                "D": "value"
            }
        }
    },
    "E": "another_value"
}

Let’s try to find the value for the key “D” using our find_key() function.

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result = find_key(example_dict, "D")
print(result)

It should return the value “value” since the key “D” exists in the nested dictionary.

value

Step 3: Test the function with non-existent keys

Finally, let’s test the function when the target key does not exist in the nested dictionary. For instance, let’s search for the key “Z”.

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result = find_key(example_dict, "Z")
print(result)

In this case, the function returns None.

None

Full Code:

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def find_key(nested_dict, target_key):
    for key, value in nested_dict.items():
        if key == target_key:
            return value
        if isinstance(value, dict):
            result = find_key(value, target_key)
            if result is not None:
                return result
 
example_dict = {
    "A": {
        "B": {
            "C": {
                "D": "value"
            }
        }
    },
    "E": "another_value"
}
 
result = find_key(example_dict, "D")
print(result)
 
result = find_key(example_dict, "Z")
print(result)

Conclusion

In this tutorial, we have learned how to find a specific key within a nested dictionary using a recursive function. This method can be helpful while working with complex and deeply nested data structures in Python. You can further enhance this function by incorporating error handling and validation checks to make it more robust.