Namedtuple

With tuples we store small groups of related fields together. A Point tuple, for example will have 2 coordinates: X and Y. The coordinates are part of a single unit.

To use namedtuple, we import the collections module. We specify the Type name. And we pass a string list of all the field names—these can then be directly used as fields.

An example

Here we create an Employee namedtuple with 3 fields. We pass a list to collections.namedtuple to specify field names id, title and salary.

Start We create a namedtuple by using the Employee class name returned by collections.namedtuple.

And At the end of the program we access the "title" field with the syntax e.title: no index is required.

import collections

# Specify the Employee namedtuple.
Employee = collections.namedtuple("Employee", ["id", "title", "salary"])

# Create Employee instance.
e = Employee(1, "engineer", 10000)

# Display Employee.
print(e)
print("Title is", e.title)Employee(id=1, title='engineer', salary=10000)
Title is engineer

Make method

Namedtuple offers extra methods—one of them is _make. With _make() we create a namedtuple from an iterable (like a list). The list elements are turned into tuple fields.

Tip The make method fills namedtuple fields based on the order of the list's elements. So we must be careful with ordering.

import collections

# A namedtuple type.
Style = collections.namedtuple("Style", ["color", "size", "width"])

# A list containing three values.
values = ["red", 10, 15]

# Make a namedtuple from the list.
tuple = Style._make(values)
print(tuple)
Style(color='red', size=10, width=15)

Benchmark, namedtuple

This benchmark tests how long it takes to create a namedtuple versus a regular tuple. The results are not encouraging for namedtuple.

Version 1 This version of the code creates a namedtuple with 2 items in it. The code tests the first item in an if-statement.

Version 2 Here we create a tuple (not a namedtuple). We test the first item with an if-statement here as well.

Result I found that namedtuple is several times slower in creation than a regular tuple.

import collections
import time

# The namedtuple instance.
Animal = collections.namedtuple("Animal", ["size", "color"])

print(time.time())

# Version 1: create namedtuple.
i = 0
while i < 10000000:
    a = Animal(100, "blue")
    if a[0] != 100:
        raise Exception()
    i += 1

print(time.time())

# Version 2: create tuple.
i = 0
while i < 10000000:
    a = (100, "blue")
    if a[0] != 100:
        raise Exception()
    i += 1

print(time.time())1403288922.718007
1403288936.606831  namedtuple = 13.89 s
1403288939.667796  tuple      =  3.06 s

A comparison

Even though namedtuple does not use excess memory, it involves more steps to initialize. And it requires a separate module (collections), making it harder to access.

In most programs, a tuple is a better choice than a named tuple. And for large groups of keys, a dictionary or set may be better. Namedtuple is limited in its use.