Python - Tuples

A tuple is a sequence of immutable Python objects. Tuples are sequences, just like lists. The only difference is that tuples can't be changed ie. tuples are immutable and tuples use parentheses and lists use square brackets.

Creating a tuple is as simple as putting different comma-separated values and optionally you can put these comma-separated values between parentheses also. For example:

tup1 = ('physics', 'chemistry', 1997, 2000); tup2 = (1, 2, 3, 4, 5 ); tup3 = "a", "b", "c", "d";

The empty tuple is written as two parentheses containing nothing:

tup1 = ();

To write a tuple containing a single value you have to include a comma, even though there is only one value:

tup1 = (50,);

Like string indices, tuple indices start at 0, and tuples can be sliced, concatenated and so on.

Accessing Values in Tuples:

To access values in tuple, use the square brackets for slicing along with the index or indices to obtain value available at that index:

Example:

#!/usr/bin/python tup1 = ('physics', 'chemistry', 1997, 2000); tup2 = (1, 2, 3, 4, 5, 6, 7 ); print "tup1[0]: ", tup1[0] print "tup2[1:5]: ", tup2[1:5]

This will produce following result:

tup1[0]: physics tup2[1:5]: [2, 3, 4, 5]

Updating Tuples:

Tuples are immutable which means you cannot update them or change values of tuple elements. But we able able to take portions of an existing tuples to create a new tuples as follows:

Example:

#!/usr/bin/python tup1 = (12, 34.56); tup2 = ('abc', 'xyz'); # Following action is not valid for tuples # tup1 += tup2; # So let's create a new tuple as follows tup3 = tup1 + tup2; print tup3;

This will produce following result:

(12, 34.56, 'abc', 'xyz')

Delete Tuple Elements:

Removing individual tuple elements is not possible. There is, of course, nothing wrong with putting together another tuple with the undesired elements discarded.

To explicitly remove an entire tuple, just use the del statement:

Example:

#!/usr/bin/python tup = ('physics', 'chemistry', 1997, 2000); print tup; del tup; print "After deleting tup : " print tup;

This will produce following result. Note an exception raised, this is because afterdel tup tuple does not exist any more:

('physics', 'chemistry', 1997, 2000) After deleting tup : Traceback (most recent call last): File "test.py", line 9, in <module> print tup; NameError: name 'tup' is not defined

Basic Tuples Operations:

Tuples respond to the + and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new tuple, not a string.

In fact, tuples respond to all of the general sequence operations we used on strings in the prior chapter :

Python Expression	Results	Description
len((1, 2, 3))	3	Length
(1, 2, 3) + (4, 5, 6)	(1, 2, 3, 4, 5, 6)	Concatenation
['Hi!'] * 4	('Hi!', 'Hi!', 'Hi!', 'Hi!')	Repetition
3 in (1, 2, 3)	True	Membership
for x in (1, 2, 3): print x,	1 2 3	Iteration

Indexing, Slicing, and Matrixes:

Because tuples are sequences, indexing and slicing work the same way for tuples as they do for strings.

Assuming following input:

L = ('spam', 'Spam', 'SPAM!')

Python Expression	Results	Description
L[2]	'SPAM!'	Offsets start at zero
L[-2]	'Spam'	Negative: count from the right
L[1:]	['Spam', 'SPAM!']	Slicing fetches sections

No Enclosing Delimiters:

Any set of multiple objects, comma-separated, written without identifying symbols, i.e., brackets for lists, parentheses for tuples, etc., default to tuples, as indicated in these short examples:

#!/usr/bin/python print 'abc', -4.24e93, 18+6.6j, 'xyz'; x, y = 1, 2; print "Value of x , y : ", x,y; print var;

This will reduce following result:

abc -4.24e+93 (18+6.6j) xyz Value of x , y : 1 2

Built-in Tuple Functions:

Python includes following tuple functions

SN	Function with Description
1	cmp(tuple1, tuple2) Compares elements of both tuples.
2	len(tuple) Gives the total length of the tuple.
3	max(tuple) Returns item from the tuple with max value.
4	min(tuple) Returns item from the tuple with min value.
5	tuple(seq) Converts a list into tuple.