Questions tagged [tuples]

A tuple, like a struct in some languages, is a collection of items of any type delimited with parentheses. Unlike structs, however, tuples are immutable. Many programming languages have "taken" tuples from functional programming languages like F#, where they are used very often.

In Python, for example, tuples are used to encapsulate the actual parameters of functions and methods. Tuples are related to currying of functions, which is a transformation that turns a function taking a tuple with n fields, into a n functions each taking one argument.

Creating a tuple

>>> l = [1, 'a', [28, 3.5]] #square brackets
>>> t = (1, 'a', [28, 3.5]) #round parentheses 
>>> type(t), type(l)
(<class 'tuple'>, <class 'list'>)
>>> t
(1, 'a', [6, 3.5])
>>> tuple(l)
(1, 'a', [6, 3.5])
>>> t == tuple(l)
True
>>> t == l
False

Also the statement

t = 12345, 54321, 'hello!'
 

is an example of tuple packing: the values 12345, 54321 and 'hello!' are packed together in a tuple. The reverse operation is also possible, e.g.:

>>> brian, x_ray, lemba = t

This is called, appropriately enough, tuple unpacking. Tuple unpacking requires that there be the same number of variables as items in tuple. Note that multiple assignment is really just a combination of tuple packing and tuple unpacking!

A one item tuple is created by an item in parens followed by a comma: e.g

>>> t = ('A single item tuple',)
>>> t
('A single item tuple',)

Also, tuples will be created from items separated by commas, like so:

>>> t = 'A', 'tuple', 'needs', 'no', 'parens'
>>> t
('A', 'tuple', 'needs', 'no', 'parens')

References

• Tuples and Sequences
• Tuples