Python Language Tuple

Internal

• Python Language

TODO

• TO PROCESS: PyOOP "Tuples and named tuples", "Named tuples"

Overview

A tuple is a immutable sequence type that contains zero or more elements and whose elements can be of different types. Once a tuple is defined, you can't add, delete or change items. A tuple is similar to a constant list, and could be used instead of a list, if we can afford the "list" to be immutable. Naturally, the list's mutating functions append(), insert() do not exist on tuples. There are several advantages of using a tuple instead of a list: a tuple uses less space than a list and they cannot be mutated by mistake. Positional function arguments can be grouped together and provided as a tuple in the function body (*args).

Declaration

A tuple is declared by specifying commas after each of its elements, with the exception of the empty tuple, that uses ():

empty_tuple = ()
one_element_tuple = 1,  # the trailing comma is mandatory
two_element_tuple = 1,2,   # for two or more elements, the trailing comma is optional

For aesthetic reasons, and also to make the tuple more visible, the comma-driven declaration can be enclosed in optional parentheses:

empty_tuple = ()
one_element_tuple = (1,)  # the trailing comma is mandatory
two_element_tuple = (1,2,)  # for two or more elements, the trailing comma is optional

Access a Tuple

To access the elements of a tuple, use the same bracket notation as for a list. The index is 0-based:

t = ('a', 'b', 'c')
assert 'a' == t[0]

Conversion from other Data Structures

The tuple() converts lists to tuples:

l = ['a', 'b', 'c']
t = tuple(l)
print(t)

Is that right? It may be that the tuple contain the list itself not the list's elements. Verify.

Tuple Unpacking

Assigning multiple variable at once is called "tuple unpacking":

t = (1, 'B', 3.0)
a, b, c = t
print(a)  # will print 1
print(b)  # will print 'B'
print(c)  # will print 3.0

Exchanging Variable Values

Tuples can be used to exchange to variable values without using a third temporary variable.

v1 = 'A'
v2 = 'B'
v1, v2 = v2, v1
print(v1)  # will print B
print(v2)  # will print A

Named Tuples

Named tuples can be a simple alternative to objects.