typing.NamedTuple – Improved Namedtuples

The NamedTuple class of the typing module added in Python 3.6 is the younger sibling of the namedtuple class in the collections module. The main difference being an updated syntax for defining new record types and added support for type hints. Like dictionaries, NamedTuples contain keys that are hashed to a particular value. But on the contrary, it supports both access from key-value and iteration, the functionality that dictionaries lack.

Creating a NamedTuple 

NamedTuple can be created using the following syntax:

class class_name(NamedTuple):
    field1: datatype
    field2: datatype

This is equivalent to:

class_name = collections.namedtuple('class_name', ['field1', 'field2'])

Example:

Python3

# importing the module
from typing import NamedTuple

# creating a class
class Website(NamedTuple):
    name: str
    url: str
    rating: int

# creating a NamedTuple
website1 = Website('GeeksforGeeks',
                   'geeksforgeeks.org',
                   5)

# displaying the NamedTuple
print(website1)

Output:

Website(name='GeeksforGeeks', url='geeksforgeeks.org', rating=5)

Access Operations

1. Access by index: The attribute values of namedtuple() are ordered and can be accessed using the index number, unlike dictionaries that are not accessible by index.
2. Access by keyname: Access by key name is also allowed as in dictionaries.
3. using getattr(): This is yet another way to access the value by giving namedtuple and key-value as its argument.

Example:

Python3

# importing the module
from typing import NamedTuple

# creating a class
class Website(NamedTuple):
    name: str
    url: str
    rating: int

# creating a NamedTuple
website1 = Website('GeeksforGeeks',
                   'geeksforgeeks.org',
                   5)

# accessing using index
print("The name of the website is : ", end = "")
print(website1[0])

# accessing using name
print("The URL of the website is : ", end = "")
print(website1.url)

# accessing using getattr()
print("The rating of the website is : ", end = "")
print(getattr(website1, 'rating'))

Output:

The name of the website is : GeeksforGeeks
The URL of the website is : geeksforgeeks.org
The rating of the website is : 5

The fields are immutable. So if we try to change the values, we get the attribute error:

Python3

# importing the module
from typing import NamedTuple

# creating a class
class Website(NamedTuple):
    name: str
    url: str
    rating: int

# creating a NamedTuple
website1 = Website('GeeksforGeeks',
                   'geeksforgeeks.org',
                   5)

# changing the attribute value
website1.name = "Google"

Output:

AttributeError: can't set attribute