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 i.e., 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. Following is a simple 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')
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 thedel statement. Following is a simple 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 after del tuptuple 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;
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:
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.
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