How to Get Keys from a List of Dictionaries in Python

In Python, dictionaries are a data type that allows you to store key-value pairs. These data structures are often used when we have a collection of values that are associated with a specific key.

Sometimes we come across a situation where we have a list of dictionaries or a collection of dictionaries and need to extract the keys from them. This tutorial will guide you through the process to achieve this using Python.

Step 1: Define a List of Dictionaries:

First, we’re going to define a sample list of dictionaries to work with. A list in Python can hold different types of values, including dictionaries. Here’s a simple list of dictionaries for example.

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list_of_dicts = [
    {"name": "Alice", "age": 25, "gender": "Female"},
    {"name": "Bob", "age": 30, "gender": "Male"},
    {"name": "Charlie", "age": 28, "gender": "Male"}
]

Step 2: Extract Keys from a Single Dictionary:

To get keys from a single dictionary, we can use the .keys() method. Let’s demonstrate this on the first dictionary from our list.

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first_dictionary = list_of_dicts[0]
keys = first_dictionary.keys()
print(keys)

The output of this script will be:

['name', 'age', 'gender']

Step 3: Getting Keys from Multiple Dictionaries:

If you need to get keys from more than one dictionary, you can use a loop. Let’s extract the keys from all dictionaries in our list.

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all_keys = list(set().union(*[d.keys() for d in list_of_dicts]))
print(all_keys)

The output will be:

['name', 'age', 'gender']

What we have done here is first extract the keys from each dictionary using list comprehension. Then, we are using the set().union() function to combine all the keys from the different dictionaries into one unique set of keys. This ensures that even if some dictionaries share the same keys, each key only appears in the final list once.

Full Code:

Here is the full code that combines all these steps:

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list_of_dicts = [
    {"name": "Alice", "age": 25, "gender": "Female"},
    {"name": "Bob", "age": 30, "gender": "Male"},
    {"name": "Charlie", "age": 28, "gender": "Male"}
]
 
first_dictionary = list_of_dicts[0]
keys = first_dictionary.keys()
print(keys)
 
all_keys = list(set().union(*[d.keys() for d in list_of_dicts]))
print(all_keys)

The output will be

dict_keys(['name', 'age', 'gender'])
['name', 'gender', 'age']

Conclusion

In conclusion, Python provides efficient ways to get keys from a list of dictionaries using built-in methods such as the .keys() method and more. These techniques can be easily extended to handle more complex cases as needed and serve as a fundamental concept that is useful to understand for any budding Python programmer.