152. collections.namedtuple for Immutable Objects

Here are 10 Python snippets demonstrating the use of collections.namedtuple for creating lightweight, immutable objects with named fields. Each snippet is separated by a delimiter.

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Snippet 1: Creating a Point with namedtuple

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from collections import namedtuple

Point = namedtuple('Point', ['x', 'y'])
p = Point(3, 4)
print(p)          # Output: Point(x=3, y=4)
print(p.x, p.y)   # Output: 3 4

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Snippet 2: Immutable Nature of namedtuple

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from collections import namedtuple

Car = namedtuple('Car', ['make', 'model', 'year'])
car = Car('Toyota', 'Corolla', 2020)

# Access fields
print(car.make)  # Output: Toyota

# Attempting to modify will raise an error
try:
    car.year = 2022
except AttributeError as e:
    print(e)  # Output: "can't set attribute"

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Snippet 3: Adding Defaults Using _replace

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from collections import namedtuple

Person = namedtuple('Person', ['name', 'age'])
default_person = Person('John Doe', 30)

# Create a new instance with some fields replaced
updated_person = default_person._replace(age=35)
print(updated_person)  # Output: Person(name='John Doe', age=35)

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Snippet 4: Using _fields and _asdict

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from collections import namedtuple

Book = namedtuple('Book', ['title', 'author', 'price'])
book = Book('1984', 'George Orwell', 19.99)

# Get field names
print(book._fields)  # Output: ('title', 'author', 'price')

# Convert to a dictionary
print(book._asdict())  # Output: {'title': '1984', 'author': 'George Orwell', 'price': 19.99}

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Snippet 5: Inheriting and Adding Methods to namedtuple

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from collections import namedtuple

class Rectangle(namedtuple('Rectangle', ['length', 'width'])):
    def area(self):
        return self.length * self.width

rect = Rectangle(5, 10)
print(rect.area())  # Output: 50

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Snippet 6: Creating a Named Tuple with Defaults

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from collections import namedtuple

Employee = namedtuple('Employee', ['name', 'position', 'salary'], defaults=['Unknown', 50000])
e1 = Employee('Alice', 'Developer')
e2 = Employee('Bob')
print(e1)  # Output: Employee(name='Alice', position='Developer', salary=50000)
print(e2)  # Output: Employee(name='Bob', position='Unknown', salary=50000)

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Snippet 7: Unpacking a Named Tuple

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from collections import namedtuple

Coordinate = namedtuple('Coordinate', ['x', 'y', 'z'])
coord = Coordinate(1, 2, 3)

x, y, z = coord
print(x, y, z)  # Output: 1 2 3

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Snippet 8: Nested namedtuple

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from collections import namedtuple

Address = namedtuple('Address', ['city', 'state'])
Person = namedtuple('Person', ['name', 'age', 'address'])

address = Address('New York', 'NY')
person = Person('Alice', 30, address)

print(person)              # Output: Person(name='Alice', age=30, address=Address(city='New York', state='NY'))
print(person.address.city) # Output: New York

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Snippet 9: Named Tuple for Storing Database Records

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from collections import namedtuple

Record = namedtuple('Record', ['id', 'name', 'email'])
data = [
    Record(1, 'Alice', '[e-mail]'),
    Record(2, 'Bob', '[e-mail]'),
]

for record in data:
    print(record.id, record.name, record.email)

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Snippet 10: Using _make to Create a Named Tuple from a List

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from collections import namedtuple

Product = namedtuple('Product', ['id', 'name', 'price'])
data = [101, 'Laptop', 999.99]

product = Product._make(data)
print(product)  # Output: Product(id=101, name='Laptop', price=999.99)

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