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Python Dictionaries

By Abhishek Jain Last updated : December 21, 2024

In this tutorial, we will learn about the Python dictionaries with the help of examples.

What is a dictionary in Python?

A dictionary is a mapping between a set of indices (keys) and a set of values. It is an extremely useful data storage construct where each element is accessed by a unique key.

A dictionary is like a list, just different in indexing. In a list, an index value is an integer, while in a dictionary index value can be any other data type called keys. It stores and retrieves the key-value pairs, where each value is indexed by a unique key.

Syntax

Dictionary = {'key1': 'value1','key2': 'value2',...,'keyn': 'valuen'}

Example

X= {'a' :"apple", 'b' :"ball", 'c' :"cat"}

print(X)

Output

{'a' :'apple', 'b' :'ball', 'c' :'cat'}

In the above example, we have created a list where each alphabet maps a English word i.e., keys are in characters (alphabets) and values are in strings.

Create an empty dictionary

We can create a dictionary using built-in function dict(), which creates a new dictionary with no items. We can also create dictionary using {}.

Example

alphabets = dict()

print(alphabets)

Output

{}

Where, {} represents empty dictionary.

Initialize and access the elements of a dictionary

To initialize or add an item to the dictionary, square brackets with unique keys are used.

Example

# Creating an empty dictionary
alphabets = dict()

# Adding elements
alphabets['a']="apple"
alphabets['b']="ball"
alphabets['c']="cat"
alphabets['e']="elephant"
alphabets['d']="dog"

# Printing the dictionary
print("alphabets:",alphabets)

# Accessing elements by keys
print("Accessing elements by keys...")
print("alphabets['a']:", alphabets['a'])
print("alphabets['b']:", alphabets['b'])
print("alphabets['c']:", alphabets['c'])
print("alphabets['d']:", alphabets['d'])
print("alphabets['e']:", alphabets['e'])

Output

alphabets: {'a': 'apple', 'b': 'ball', 'c': 'cat', 'e': 'elephant', 'd': 'dog'}
Accessing elements by keys...
alphabets['a']: apple
alphabets['b']: ball
alphabets['c']: cat
alphabets['d']: dog
alphabets['e']: elephant

Note: May you observe the order of the key-value pairs is not in same order (i.e., input and output orders are not same). Because the order of items in a dictionary is unpredictable.

Traverse/Iterate through a dictionary

Traversing refers to visiting each element index at least one to access its value. This can be done using looping or say by using 'for-loop'.

Example

# Creating an empty dictionary
alphabets = dict()

# Adding elements
alphabets['a']="apple"
alphabets['b']="ball"
alphabets['c']="cat"
alphabets['e']="elephant"
alphabets['d']="dog"

# Printing the dictionary
print("alphabets:",alphabets)

# Traverse/Iterate through a dictionary
print("\nTraverse/Iterate through a dictionary...")
for alphabet in alphabets:
    print(alphabets[alphabet])

Output

alphabets: {'a': 'apple', 'b': 'ball', 'c': 'cat', 'e': 'elephant', 'd': 'dog'}

Traverse/Iterate through a dictionary...
apple
ball
cat
elephant
dog

As said previously, the order of items in a dictionary is unpredictable.

Length of a dictionary

To find the length of a dictionary i.e., the total number of elements of a dictionary, use the len() method. It returns the total number of elements of a dictionary.

Example

# Creating  dictionary
alphabets = {"a": "apple", "b": "ball", "c": "cat", "d": "dog"}

# Printing the dictionary
print("alphabets:", alphabets)

# Length of the dictionary
print("The total elements are:", len(alphabets))

Output

alphabets: {'a': 'apple', 'b': 'ball', 'c': 'cat', 'd': 'dog'}
The total elements are: 4

Create dictionary using the dict() constructor

A dictionary can also be created using the dict() constructor by providing the keys and values.

Example

# Creating  dictionary
alphabets = dict(a="apple", b="ball", c="cat", d="dog")

# Printing the dictionary
print("alphabets:", alphabets)

Output

alphabets: {'a': 'apple', 'b': 'ball', 'c': 'cat', 'd': 'dog'}

Dictionary with items of different data types

A dictionary can also have items of different data types such as strings, integers, Booleans, etc. It may also have a dictionary itself.

Example

# Creating dictionary with different items
# of different data types
student = {
    "rollNo": 101,
    "name": "Raghav",
    "perc": 85.90,
    "isMonitor": False,
    "dob": {"dd": 10, "mm": 7, "yy": 2002},
}

# Printing the dictionary
print("student:", student)

Output

student: {'rollNo': 101, 'name': 'Raghav', 'perc': 85.9, 'isMonitor': False, 'dob': {'dd': 10, 'mm': 7, 'yy': 2002}}

Type of dictionary and its items

The type of a dictionary is <class 'dict'> that can be found using the type() method. In the below example, we will print the type of the dictionary and its items.

Example

# Creating dictionary with different items
# of different data types

student = {
    "rollNo": 101,
    "name": "Raghav",
    "perc": 85.90,
    "isMonitor": False,
    "dob": {"dd": 10, "mm": 7, "yy": 2002},
}

# Printing the dictionary
print("student:", student)
print()

# Printing types
print("Type of student:", type(student))
print("Type of student['rollNo']:", type(student['rollNo']))
print("Type of student['name']:", type(student['name']))
print("Type of student['perc']:", type(student['perc']))
print("Type of student['isMonitor']:", type(student['isMonitor']))
print("Type of student['dob']:", type(student['dob']))

Output

student: {'rollNo': 101, 'name': 'Raghav', 'perc': 85.9, 'isMonitor': False, 'dob': {'dd': 10, 'mm': 7, 'yy': 2002}}

Type of student: <class 'dict'>
Type of student['rollNo']: <class 'int'>
Type of student['name']: <class 'str'>
Type of student['perc']: <class 'float'>
Type of student['isMonitor']: <class 'bool'>
Type of student['dob']: <class 'dict'>