What Is a Mapping Data Type in Python?


Heather Bennett

In Python, the mapping data type is a built-in container that stores a collection of key-value pairs. It is used to represent relationships between unique keys and their associated values. This data type is commonly referred to as a dictionary.

Defining a Mapping Data Type

A mapping data type in Python is defined using curly braces ({}) with key-value pairs separated by colons (:). The keys within the mapping must be unique, while the values can be of any data type.

Here’s an example of creating a mapping data type:

<code>my_dict = {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}</code>

Accessing Values in a Mapping

To access the values stored in a mapping, you can use the key as an index. If the specified key does not exist, it will result in a KeyError. Here’s an example:

<code>my_dict = {'name': 'John', 'age': 25, 'city': 'New York'}
print(my_dict['name'])  # Output: John
print(my_dict['occupation'])  # Raises KeyError: 'occupation'</code>

Modifying Values in a Mapping

You can modify the value associated with a specific key in a mapping by directly assigning a new value to it. Here’s an example:

<code>my_dict = {'name': 'John', 'age': 25, 'city': 'New York'}
my_dict['age'] = 30
print(my_dict)  # Output: {'name': 'John', 'age': 30, 'city': 'New York'}</code>

Adding and Removing Key-Value Pairs

To add a new key-value pair to a mapping, you can simply assign a value to a new key. To remove a key-value pair, you can use the del keyword followed by the key. Here are examples:

<code>my_dict = {'name': 'John', 'age': 25}
my_dict['occupation'] = 'Engineer'
print(my_dict)  # Output: {'name': 'John', 'age': 25, 'occupation': 'Engineer'}

del my_dict['age']
print(my_dict)  # Output: {'name': 'John', 'occupation': 'Engineer'}</code>

Iterating Through a Mapping

You can iterate through the keys, values, or both in a mapping using loops. The keys(), values(), and items() methods of the mapping object provide access to these elements.

<code>my_dict = {'name': 'John', 'age': 25}

# Iterating through keys
for key in my_dict.keys():

# Iterating through values
for value in my_dict.values():

# Iterating through both keys and values
for key, value in my_dict.items():
    print(key, value)</code>

Nested Mappings

A mapping data type can also contain other mappings as its values. This is known as nesting. By using nested mappings, you can represent more complex relationships and hierarchical data structures.

Here’s an example of a nested mapping:

<code>my_dict = {'person1': {'name': 'John', 'age': 25},
           'person2': {'name': 'Jane', 'age': 30}}

print(my_dict['person1']['name'])  # Output: John
print(my_dict['person2']['age'])  # Output: 30</code>


In Python, the mapping data type (dictionary) is a powerful tool for storing and manipulating key-value pairs. It allows you to represent relationships between unique keys and values, and provides methods for accessing, modifying, adding, removing, and iterating through the data. Understanding how to effectively utilize this data type will greatly enhance your programming capabilities.

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