Tuple in Python

Tuples are used for grouping data.A tuple is an immutable list, i.e. a tuple cannot be changed in any way once it has been created. A tuple is defined analogously to lists, except that the set of elements is enclosed in parentheses instead of square brackets. The rules for indices are the same as for lists. Once a tuple has been created, you can't add elements to a tuple or remove elements from a tuple.

Where is the benefit of tuples?

Tuples are faster than lists.

If you know that some data doesn't have to be changed, you should use tuples instead of lists, because this protects your data against accidental changes.

Tuples can be used as keys in dictionaries, while lists can't.

The following example shows how to define a tuple and how to access a tuple. 

Furthermore we can see that we raise an error, if we try to assign a new value to an element of a tuple:

Tuple creation

>>> t = ("tuples", "are", "immutable")

>>> t[0]

'tuples'

>>> t[0]="assignments to elements are not possible"

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

TypeError: 'tuple' object does not support item assignment

To create a tuple with a single element, we have to include the final comma:

>>> t1 = (’a’,)

>>> type(t1)

<type ’tuple’>

Without the comma, Python treats (’a’) as a string in parentheses:

>>> t2 = (’a’)

>>> type(t2)

<type ’str’>

This will create an empty tuple

>>> t=()

>>> type(t)

<type 'tuple'>

>>> t=tuple()

>>> type(t)

<type 'tuple'>

This will add a new element to the Tuple

>>>t=(10,20,30)

>>>t=t+(40,)

>>>t

(10,20,30,40)

Tuple operations are similar to list

Example

>>>a=(10,20,30)

>>>b=(40,50)

>>>a+b

(10,20,30,40,50)

>>>b*2

(40,50,40,50)

>>>10 in a

True

>>>100 not in a

True

>>>c=a+(30,)

>>>c

(10,20,30,30)

Tuple Functions

>>>min(a)

10

>>>max(a)

30

>>>sum(a)

60

>>>len(a)

3

>>>a.index(20)

1

>>>c.count(30)

2

cmp( )

This is used to check whether the given tuples are same or not. If both are same, it will

return ‘zero’, otherwise return 1 or -1. If the first tuple is big, then it will return 1,

otherwise return -1.

>>>a=(10,20)

>>>b=(10,20)

>>>cmp(a,b)

0

>>>a=(100,200)

>>>b=(10,20)

>>>cmp(a,b)

1

>>>cmp(b,a)

-1

since the tuples are immutable you cannot sort the tuple.However you can use the sequence function sorted() to create a new sorted tuple.

>>>sorted(a)

Tuple packing and unpacking

tuples are used to group data. In tuple packing, the values on the right are ‘packed’ together in a tuple:

>>>stud=(101,’shilpa’,’kayamkulam’,690535) 

In tuple unpacking, the values in a tuple on the right are ‘unpacked’ into the variables/names on the left:

>>>(rno,name,place,pin)=stud

>>> rno

101

>>> name

'shilpa'

>>> place

'kayamkulam'

>>> pin

690535

Tuple assignments

Once in a while, it is useful to swap the values of two variables. With conventional assignment statements, we have to use a temporary variable. For example, to swap a and b:

temp = a

a = b

b = temp 

Tuple assignment solves this problem neatly:

(a, b) = (b, a) 

The left side is a tuple of variables; the right side is a tuple of values. Each value is assigned to its respective variable. All the expressions on the right side are evaluated before any of the assignments. This feature makes tuple assignment quite versatile.

Naturally, the number of variables on the left and the number of values on the right have to be the same:

We can swap values of two tuples

>>>t1=(10,20,30)

>>>t2=(100,200)

>>>t2,t1=t1,t2

>>>t1

(100,200)

>>>t2

(10,20,30)

Converting tuples into lists and lists into tuples

>>>L=[10,20,30,40]

>>>T=tuple(L)

>>>T

(10,20,30,40)

>>> T=(10,20,30)

>>> L=list(T)

>>> L

[10, 20, 30]

Sample Program

Program to read numbers and find minimum, maximum and sum using Tuple

n=input("Enter how many numbers....")

print "Enter {} numbers".format(n)

t=tuple()

for i in range(n):

   x=input()

    t=t+(x,)

print "minimum=",min(t)

print "maximum=",max(t)

print "sum=",sum(t)

Now you can try following programs using tuple

1.Read ‘n’ numbers and find their sum,average,min,max and also print a sorted list.

2.Read two tuples and exchange their values.

3.Find the variance and standard deviation of ‘n’ numbers.

4.Check the number of occurrence of an element in a tuple.

5.Find the positions of occurrences(indices) of an element in a tuple.