Dictionary in Python

In this tutorial, we will learn about the dictionary data type in Python. We will also learn how to create a dictionary, access its elements, and perform various operations on it.

Table Of Contents

1. Python Dictionary
   1. Creating a Dictionary
   2. Accessing Dictionary Elements
2. Adding Elements to Dictionary
   1. Updating Dictionary Elements
3. Deleting Dictionary Elements
4. Iterating Through Dictionary
5. Dictionary Methods
6. Quiz
7. Conclusion

Python Dictionary

A dictionary is a collection of key-value pairs. It is an unordered and mutable data type (that can be changed). It is represented by curly braces {}.

It is similar to a list, but instead of using indexes to access elements, we use keys. The keys are unique and immutable. The values can be of any data type and can be duplicated.

Let's see an example of a dictionary.

fruits = {
  "apple": 10,
  "banana": 20,
  "orange": 30,
  "grapes": 10
}
print(fruits)

{'apple': 10, 'banana': 20, 'orange': 30, 'grapes': 10}

Here, the keys are the names of the fruits and the values are their prices. We can access the values by using the keys.

Creating a Dictionary

We can create a dictionary in 2 different ways.

1. Using curly braces {} - It is the most common way to create a dictionary. We can create an empty dictionary using curly braces.
2. Using the dict() function - It takes a list of tuples as an argument and returns a dictionary.

Let's see an example of both methods.

# 1. Using curly braces
fruits = {
  "apple": 10,
  "banana": 20,
  "orange": 30
}
print(fruits)

# 2. Using dict() function
fruits = dict([
  ("apple", 10),
  ("banana", 20),
  ("orange", 30)
])
print(fruits)

{'apple': 10, 'banana': 20, 'orange': 30}
{'apple': 10, 'banana': 20, 'orange': 30}

Note: In python dictionary key can be any immutable type including tuple, string, number, boolean, etc. But not list, set, dictionary, etc as they are mutable. But it is recommended to use string as a key in dictionary.

Accessing Dictionary Elements

We can use 2 different ways to access the elements of a dictionary.

1. Using the get() method - It takes the key as an argument and returns the value associated with it.
2. Using the square brackets - It is similar to accessing elements of a list. We use the key inside the square brackets to access the value.

Let's see an example of both methods.

fruits = {
  "apple": 10,
  "banana": 20,
  "orange": 30,
  "grapes": 10
}
# 1. Using get() method
print("Price of apple is", fruits.get("apple"))
# 2. Using square brackets
print("Price of banana is", fruits["banana"])

Price of apple is 10
Price of banana is 20

Adding Elements to a Dictionary

Dictionary is a mutable data type. We can add new elements to it.

To add a new element, use the square brackets, pass a new key and assign a value to it.

Let's see an example.

fruits = {
  "apple": 10,
  "banana": 20
}
print("Before adding new fruit:", fruits)

# Add a new fruit
fruits["orange"] = 30
print("After adding new fruit:", fruits)

Before adding new fruit: {'apple': 10, 'banana': 20}
After adding new fruit: {'apple': 10, 'banana': 20, 'orange': 30}

Note: If the key already exists, the value will be updated.

Updating Items in a Dictionary

We have in 2 different ways to update items in a dictionary. First using the above method and second using the update() method.

The update() method takes a dictionary as an argument and updates the dictionary with the new values.

Let's see an example of this.

fruits = {
  "apple": 10,
  "banana": 20,
  "orange": 30
}
print("Before updating:", fruits)

# Update the price of apple
fruits["apple"] = 15
print("After updating:", fruits)

Before updating: {'apple': 10, 'banana': 20, 'orange': 30}
After updating: {'apple': 15, 'banana': 20, 'orange': 30}

Note: If the key doesn't exist, a new element will be added to the dictionary.

Removing items from a Dictionary

Here are 3 different ways to remove items from a dictionary.

1. Using the pop() method - It takes the key as an argument and removes the element associated with it. It returns the value of the removed element.

   Example

   Let's remove the apple from the dictionary.

   fruits = {
     "apple": 10,
     "banana": 20,
     "orange": 30
   }
   print("Before removing:", fruits)
   
   # Removing apple
   fruits.pop("apple")
   print("After removing apple:", fruits)
   
   # Removing banana
   fruits.pop("banana")
   print("After removing banana:", fruits)

   Before removing: {'apple': 10, 'banana': 20, 'orange': 30}
   After removing apple: {'banana': 20, 'orange': 30}
   After removing banana: {'orange': 30}

2. Using the popitem() method - It removes the last inserted element from the dictionary. It returns the key and value of the removed element as a tuple.

   Example

   Let's remove the last inserted element from the dictionary.

   fruits = {
     "apple": 10,
     "banana": 20,
     "orange": 30
   }
   print("Before removing:", fruits)
   
   # Removing the last inserted element
   fruits.popitem()
   print("After removing:", fruits)

   Before removing: {'apple': 10, 'banana': 20, 'orange': 30}
   After removing: {'apple': 10, 'banana': 20}

3. Using the del keyword - It removes the element associated with the key passed as an argument. It doesn't return any value.

   Example

   Removing apple from the dictionary.

   fruits = {
     "apple": 10,
     "banana": 20,
     "orange": 30
   }
   
   # Removing apple
   del fruits["apple"]
   print(fruits)

   {'banana': 20, 'orange': 30}

Iterating Through a Dictionary

There are multiple different ways to access the elements in a dictionary.

for loop in Python is the most common way to iterate through a dictionary.

Let's see 3 different ways to iterate through a dictionary.

fruits = {
  "apple": 10,
  "banana": 20
}

# Iterating through the dictionary
print("Method 1: using items() method")
for key, value in fruits.items():
    print(key, value)
    
print("Method 2: using keys() method")
for key in fruits.keys():
    print(key, fruits[key])

print("Method 3: access keys directly")
for key in fruits:
    print(key, fruits[key])

Method 1: using items() method
('apple', 10)
('banana', 20)
Method 2: using keys() method
('apple', 10)
('banana', 20)
Method 3: access keys and values directly
('apple', 10)
('banana', 20)

Dictionary Methods

There are many built-in methods available for dictionaries. Each method has a different purpose.

Let's see some of the most commonly used methods with their usage.