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Dictionaries

Dictionaries are unordered collections of key-value pairs. They are commonly used to store and retrieve data based on some unique identifier, known as a key. Keys are used to identify and access values in a dictionary, but unlike lists, they are not used to define order.

Creating a dictionary is simple. Enclose key-value pairs in curly braces {} separated by colons :

person = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

Accessing and Modifying Values​

You can access a value by providing its key in square brackets.

name = person["name"]
# this accesses the value 'Alice'

To modify a value, access the key and assign a new value.

person["age"] = 26

Dictionary Methods​

Python provides various methods to manipulate dictionaries.

Adding and Updating Elements​

dict[key] = value : Adds a new key-value pair or updates an existing one. dict.update(another_dict) : Updates the dictionary with elements from another dictionary.

Removing Elements​

del dict[key] : Removes the specified key-value pair. dict.pop(key) : Removes and returns the value associated with the key.

Retrieving Values Safely​

dict.get(key) : Retrieves the value for the specified key. Returns None if the key doesn't exist.

Iterating Through Keys and Values​


for key in person:
    print(key, person[key])

Other Useful Methods​

dict.keys() : Returns a list of keys. dict.values() : Returns a list of values. dict.items() : Returns a list of key-value pairs.

Use Cases of Dictionaries​

Dictionaries find applications in various scenarios:

  • Storing Configuration Settings: Dictionaries are great for storing settings with descriptive keys.
  • Counting Occurrences: Count the frequency of words in a text by using words as keys and counts as values.
  • Data Organization: Organize data retrieved from databases or APIs with meaningful keys.
  • Caching: Store computed results for efficient retrieval.
  • JSON-like Structures: Dictionaries are the basis of JSON data format.