Advanced Tuple Concepts

A tuple of numbers can be used as a dictionary key to map a coordinate to a location name.

The location is New York City.

If a tuple contains a mutable object like a list, it becomes unhashable and will raise a TypeError if you try to use it as a dictionary key.

Error: unhashable type: 'list'

collections.namedtuple

This is the classic factory function for creating simple, lightweight, immutable records. It returns a new tuple subclass with named fields.

Make: Toyota
Model: Camry
Year (by index): 2022

typing.NamedTuple

Introduced in Python 3.6, this is the modern, type-hinted way to create named tuples. It uses class syntax and provides better static analysis support for tools like MyPy.

Point coordinates: (10.5, -5.2)

dataclasses.dataclass(frozen=True)

For more complex objects, dataclasses are the standard. Setting frozen=True makes instances immutable, giving them tuple-like data integrity while allowing for default values, methods, and more.

User(user_id=1, username='admin', is_active=True)
Error: cannot assign to field 'is_active'

Composite Sort Keys

Because tuples are compared lexicographically, they are perfect for creating composite sort keys. The sorted() function will use the first element of the tuple to sort, then the second as a tie-breaker, and so on.

[('Bob', 'A'), ('Alice', 'B'), ('Charlie', 'B')]

Database APIs

Many Python database drivers (following the PEP 249 standard) return query results as a list of tuples, where each tuple represents a row. This is a natural fit, as database rows are fixed records that shouldn’t be mutated accidentally.

import sqlite3
 
# Example setup (conceptual)
conn = sqlite3.connect(":memory:")
cursor = conn.cursor()
cursor.execute("CREATE TABLE users (id INT, name TEXT)")
cursor.execute("INSERT INTO users VALUES (1, 'Alice'), (2, 'Bob')")
 
# Fetching data returns a list of tuples
cursor.execute("SELECT * FROM users")
rows = cursor.fetchall()
 
print(rows)
# Expected output: [(1, 'Alice'), (2, 'Bob')]
 
for user_id, name in rows:
    print(f"Processing user {user_id}: {name}")