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PYTHON - TUPLES

A tuple is a sequence of immutable Python objects. Tuples are sequences, just like lists. The differences between tuples and lists are, the tuples cannot be changed unlike lists and tuples use parentheses, whereas lists use square brackets.

Creating a tuple is as simple as putting different comma-separated values. 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 they 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. For 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]

When the above code is executed, it produces the following result:

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

Updating Tuples

Tuples are immutable which means you cannot update or change the values of tuple elements. You are able to take portions of existing tuples to create new tuples as the following example demonstrates:

#!/usr/bin/python
tup1 = (12, 34.56);
tup2 = ('abc', 'xyz');
# Following action is not valid for tuples
# tup1[0] = 100;
# So let's create a new tuple as follows
tup3 = tup1 + tup2;
print tup3;

When the above code is executed, it produces the following result:

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

Deleting 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. For example:

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

This produces the following result. Note an exception raised, this is because after del tup, tuple does not exist anymore:

('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;

When the above code is executed, it produces the following result:

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

Built-in Tuple Functions

Python includes the following tuple functions:

Sr. No.	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.

Let us go through tuple functions briefly:

Cmp(tuple1, tuple2)

Description

The method cmp() compares elements of two tuples.

Syntax

Following is the syntax for cmp() method:

cmp(tuple1, tuple2)

Parameters

tuple1 -- This is the first tuple to be compared
tuple2 -- This is the second tuple to be compared

Return Value

If elements are of the same type, perform the compare and return the result. If elements are different types, check to see if they are numbers.

If numbers, perform numeric coercion if necessary and compare.
If either element is a number, then the other element is "larger" (numbers are "smallest").
Otherwise, types are sorted alphabetically by name.

If we reached the end of one of the tuples, the longer tuple is "larger." If we exhaust both tuples and share the same data, the result is a tie, meaning that 0 is returned.

Example

The following example shows the usage of cmp() method.

#!/usr/bin/python
tuple1, tuple2 = (123, 'xyz'), (456, 'abc')
print cmp(tuple1, tuple2);
print cmp(tuple2, tuple1);
tuple3 = tuple2 + (786,);
print cmp(tuple2, tuple3)

When we run above program, it produces following result:

-1
1
-1

54. Len(tuple)

Description

The method len() returns the number of elements in the tuple.

Syntax

Following is the syntax for len() method:

len(tuple)

Parameters

tuple -- This is a tuple for which number of elements to be counted.

Return Value

This method returns the number of elements in the tuple.

Example

The following example shows the usage of len() method.

#!/usr/bin/python
tuple1, tuple2 = (123, 'xyz', 'zara'), (456, 'abc')
print "First tuple length : ", len(tuple1);
print "Second tuple length : ", len(tuple2);

When we run above program, it produces following result:

First tuple length : 3
Second tuple length : 2

55. Max(tuple)

Description

The method max() returns the elements from the tuple with maximum value.

Syntax

Following is the syntax for max() method:

max(tuple)

Parameters

tuple -- This is a tuple from which max valued element to be returned.

Return Value

This method returns the elements from the tuple with maximum value.

Example

The following example shows the usage of max() method.

#!/usr/bin/python
tuple1, tuple2 = (123, 'xyz', 'zara', 'abc'), (456, 700, 200)
print "Max value element : ", max(tuple1);
print "Max value element : ", max(tuple2);

When we run above program, it produces following result:

Max value element : zara
Max value element : 700

56. Min(tuple)

Description

The method min() returns the elements from the tuple with minimum value.

Syntax

Following is the syntax for min() method:

min(tuple)

Parameters

tuple -- This is a tuple from which min valued element to be returned.

Return Value

This method returns the elements from the tuple with minimum value.

Example

The following example shows the usage of min() method.

#!/usr/bin/python
tuple1, tuple2 = (123, 'xyz', 'zara', 'abc'), (456, 700, 200)
print "min value element : ", min(tuple1);
print "min value element : ", min(tuple2);

When we run above program, it produces following result:

min value element : 123
min value element : 200

57. Tuple(seg)

Description

The method tuple() compares elements of two tuples.

Syntax

Following is the syntax for tuple() method:

tuple( seq )

Parameters

seq -- This is a tuple to be converted into tuple.

Return Value

This method returns the tuple.

Example

The following example shows the usage of tuple() method.

#!/usr/bin/python
aList = (123, 'xyz', 'zara', 'abc');
aTuple = tuple(aList)
print "Tuple elements : ", aTuple

When we run above program, it produces following result:

Tuple elements : (123, 'xyz', 'zara', 'abc')

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PYTHON - TUPLES