What are python dictionaries?
A Python dictionary is an unordered collection of items where every item is a key/value pair.
Creating a dictionary
-
To create a python dictionary, simply place
items key: value/pairs -
Keys must be immutable for an item in a dictionary, whereas values can be of any datatypes.
Below are different ways to create a dictionary.
# empty dictionaryempty_dict = {}print("Empty dictionary --> "+ str(empty_dict))# dictionary with itemsfruits = {1:"Apple",2:"Orange"}print("fruits dictionary --> "+ str(fruits))# using built in dict() functionpets = dict({1:"Cat",2:"Dog"})print("pets dictionary --> "+ str(pets))
Accessing elements from a dictionary
Python dictionary uses Keys to access items such as:
- Square brackets
[] - The
get()method
Interpreter may throw
KeyError, if a key is not found in dictionary when we use square brackets[]. However, theget()method returnsNone.
It’s always safer to use the get() method.
fruits = {1:"Apple",2:"Orange"}print(fruits[1])print(fruits.get(1))# returns Noneprint(fruits.get(3))# Raises KeyError since 3 is not a key in fruits dictionaryprint(fruits[3])
Adding or removing items
We can add new items or change the value of existing items using the assignment = operator.
Use the pop() method to remove an item from a dictionary. It takes key as a parameter and returns the value of the item that is removed.
fruits = {1:"Apple",2:"Orange"}print("Original fruits dict --> "+str(fruits))# add new itemfruits[3] = "Banana"print("Added 'Banana' to fruits dict --> "+str(fruits))# change value of an itemfruits[2] = "Grapes"print("Change Value at index 2 in fruits dict --> "+str(fruits))# removes item and returns itfruits.pop(1)print("Remove element at index 1 fruits dict --> "+str(fruits))
When to use python dictionaries
We have other data structures like List, Set etc., in Python. Therefore, it is important to know when to use dictionaries.
- Python dictionaries are optimized versions of HashMap.
- HashMaps are developed for faster lookups.
- Use Python dictionaries when there is a need to search elements faster.
Time complexity to set, get and delete an item in dictionary is
