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
- 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
- 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
- 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
- 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')
###################################
Tuple
A tuple is a collection which is ordered and unchangeable. In Python tuples are written with round brackets.
Example
Create a Tuple:
thistuple = ("apple", "banana", "cherry")
print(thistuple)
Access Tuple Items
You can access tuple items by referring to the index number, inside square brackets:
Example
Return the item in position 1:
thistuple = ("apple", "banana", "cherry")
print(thistuple[1])
Change Tuple Values
Once a tuple is created, you cannot change its values. Tuples are unchangeable.
Loop Through a Tuple
You can loop through the tuple items by using a for loop.
Example
Iterate through the items and print the values:
thistuple = ("apple", "banana", "cherry")
for x in thistuple:
print(x)
Check if Item Exists
To determine if a specified item is present in a tuple use the in keyword:
Example
Check if "apple" is present in the tuple:
thistuple = ("apple", "banana", "cherry")
if "apple" in thistuple:
print("Yes, 'apple' is in the fruits tuple")
Tuple Length
To determine how many items a tuple has, use the len() method:
Example
Print the number of items in the tuple:
thistuple = ("apple", "banana", "cherry")
print(len(thistuple))
Add Items
Once a tuple is created, you cannot add items to it. Tuples are unchangeable.
Example
You cannot add items to a tuple:
thistuple = ("apple", "banana", "cherry")
thistuple[3] = "orange" # This will raise an error
print(thistuple)
Remove Items
Note: You cannot remove items in a tuple.
Tuples are unchangeable, so you cannot remove items from it, but you can delete the tuple completely:
Example
The del keyword can delete the tuple completely:
thistuple = ("apple", "banana", "cherry")
del thistuple
print(thistuple) #this will raise an error because the tuple no longer exists
The tuple() Constructor
It is also possible to use the tuple() constructor to make a tuple.
Example
Using the tuple() method to make a tuple:
thistuple = tuple(("apple", "banana", "cherry")) # note the double round-brackets
print(thistuple)
Tuple Methods
Python has two built-in methods that you can use on tuples.
| Method | Description |
|---|---|
| count() | Returns the number of times a specified value occurs in a tuple |
| index() | Searches the tuple for a specified value and returns the position of where it was found |
###########################3
To find max,min etc elements in the tuple must be of the same type
> t=(1,'a',1,2)
>>> t.count(1)
2>>> t.index('a')
1