A Python dictionary is a data structure that stores the value in key: value pairs. Values in a dictionary can be of any data type and can be duplicated, whereas keys can’t be repeated and must be immutable.

Example: Here, the data is stored in key: value pairs in dictionaries, which makes it easier to find values.

Python 

d = {1: 'Codes', 2: 'For', 3: 'Codes'}
print(d)

{1: 'Codes', 2: 'For', 3: 'Codes'}

How to Create a Dictionary

In Python, a dictionary can be created by placing a sequence of elements within curly {} braces, separated by a ‘comma’.

Python

# create dictionary using { }
d1 = {1: 'Codes', 2: 'For', 3: 'Codes'}
print(d1)

# create dictionary using dict() constructor
d2 = dict(a = "Codes", b = "for", c = "Codes")
print(d2)

{1: 'Codes', 2: 'For', 3: 'Codes'}
{'a': 'Codes', 'b': 'for', 'c': 'Codes'}

• From Python 3.7 Version onward, Python dictionary is Ordered.
• Dictionary keys are case sensitive: the same name but distinct cases of Key will be treated distinctly.
• Keys must be immutable: This means keys can be strings, numbers, or tuples but not lists.
• Keys must be unique: Duplicate keys are not allowed, and any duplicate key will overwrite the previous value.
• Dictionary internally uses Hashing. Hence, operations similar as search, insert, delete can be performed in Constant Time.

Accessing Dictionary Items

We can access a value from a dictionary by using the key within square brackets orget()method.

Python 

d = { "name": "Alice", 1: "Python", (1, 2): [1,2,4] }
# Access using key
print(d["name"])

# Access using get()
print(d.get("name"))  

Alice
Alice

Adding and Updating Dictionary Items

We can add new key-value pairs or update existing keys by using assignment.

Python 

d = {1: 'Codes', 2: 'For', 3: 'Codes'}
# Adding a new key-value pair
d["age"] = 22

# Updating an existing value
d[1] = "Python dict"

print(d)

{1: 'Python dict', 2: 'For', 3: 'Codes', 'age': 22}

Removing Dictionary Items

We can remove items from dictionary using the following methods:

• del: Removes an item by key.
• pop(): Removes an item by key and returns its value.
• clear(): Empties the dictionary.
• popitem(): Removes and returns the last key-value pair.

Python 

d = {1: 'Codes', 2: 'For', 3: 'Codes', 'age':22}
# Using del to remove an item
del d["age"]
print(d)

# Using pop() to remove an item and return the value
val = d.pop(1)
print(val)

# Using popitem to removes and returns
# the last key-value pair.
key, val = d.popitem()
print(f"Key: {key}, Value: {val}")

# Clear all items from the dictionary
d.clear()
print(d)

{1: 'Codes', 2: 'For', 3: 'Codes'}
codes
Key: 3, Value: Codes
{}

Iterating Through a Dictionary

We can iterate over keys [using keys() method] , values [using values() method] or both [using item() method] with a for loop.

Python 

d = {1: 'Codes', 2: 'For', 'age':22}
# Iterate over keys
for key in d:
    print(key)

# Iterate over values
for value in d.values():
    print(value)

# Iterate over key-value pairs
for key, value in d.items():
    print(f"{key}: {value}")

1
2
age
Codes
For
22
1: Codes
2: For
age: 22

Nested Dictionaries

Example of Nested Dictionary:

Python 

    d = {1: 'Codes', 2: 'For',
                     3: {'A': 'Welcome', 'B': 'To', 'C': 'Codes'}}

print(d)

{1: 'Codes', 2: 'For', 3: {'A': 'Welcome', 'B': 'To', 'C': 'Codes'}}

Python Dictionary – FAQs

How to use dictionaries in Python?

Dictionaries in Python are getting used to store key-value pairs. They are unordered, mutable, and can contain any Python objects when values.

# Creating a dictionary
my_dict = {‘key1’: ‘value1’, ‘key2’: ‘value2’}
# Accessing values by keys
print(my_dict[‘key1’]) # Output: value1

# Modifying values
my_dict[‘key2’] = ‘new_value’
# Adding new key-value pairs
my_dict[‘key3’] = ‘value3’
# Removing a key-value pair
del my_dict[‘key1’]

How to print dictionaries in Python?

You can use print() to display the contents of a dictionary. You can print the entire dictionary or specific elements by accessing keys or values.

my_dict = {‘name’: ‘Alice’, ‘age’: 30}
# Printing the entire dictionary
print(my_dict)
# Printing specific elements
print(my_dict[‘name’]) # Output: Alice

How to declare a dictionary in Python?

You can declare a dictionary by enclosing key-value pairs within curly braces {}.

# Empty dictionary
empty_dict = {}
# Dictionary with initial values
my_dict = {‘key1’: ‘value1’, ‘key2’: ‘value2’}

What are dictionary keys and values in Python?

In a dictionary, keys are unique identifiers that are getting used to access values. Values are the data associated with those keys.

my_dict = {‘name’: ‘Alice’, ‘age’: 30}
# Accessing keys and values
print(my_dict.keys()) # Output: dict_keys([‘name’, ‘age’])
print(my_dict.values()) # Output: dict_values([‘Alice’, 30])