Python: Tuples and Basic Operations on Tuples

What is a tuple? How is it different from a list? And some basic methods on Tuples

January 9, 2013 - 7 minute read -
python python-tuple

Table of Contents

What is a Tuple?

Tuple is a sequence of elements. A tuple is immutable, unlike a list in Python. By immutable, we mean that it is not possible to update a tuple after declaring one. The elements inside a tuple can be any Python object such a string, integer etc. Tuples are surrounded by parenthesis.

Examples:

>>> t1 = (1, "abc", 3.0)
>>> t1
(1, 'abc', 3.0)
>>> type(t1)
<type 'tuple'>

Declaring a Tuple

Empty Tuple is declared by empty parenthesis.

>>> t2 = ()
>>> t2
()
>>> type(t2)
<type 'tuple'>

It is important to note that declaring a tuple consisting a single element requires a comma after the first element.

>>> t3 = (1,)
>>> t3
(1,)
>>> type(t3)
<type 'tuple'>

If we miss out on that comma, t3 would become an integer because 1 itself is an integer.

>>> t3 = (1)
>>> type(t3)
<type 'int'>
>>> t3 = ('abc')
>>> type(t3)
<type 'str'>

Do keep this in mind. In future, a lot of people will judge your basic python knowledge on the above knowledge.

Accessing elements of a Tuple

We use square brackets along with the index which we want to access.

Examples:

>>> t1 = (1, "abc", 3.0)
>>> t1[0]
1
>>> t1[1]
'abc'
>>> t1[2]
3.0
>>> t1[3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: tuple index out of range

If you try accessing some index that doesn’t exist, Python raises appropriate error. We can also access elements using negative indexing.

>>> t1[-1]
3.0
>>> t1[-2]
'abc'

Index table indicating positive and negative index values.

---------------------------
tuple      |  1  "abc"  3.0
+ve index  |  0     1     2
-ve index  | -3    -2    -1
---------------------------

Updating elements of a Tuple

We saw in the definition of a tuple that tuples are immutable. It is not possible to update them once declared. but what happens if we try to do so?

>>> t1 = (1, "abc", 3.0)
>>> t1[1] = 'xyz'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

If we try to update the element by using index, it raises an error saying that ‘tuple’ object does not support item assignment.

However, if you add mutable elements such as a list inside a tuple, we can mutate them. For example:

>>> a = [1, 2]
>>> b = [4, 5]
>>> t = (a, b)
>>> t
([1, 2], [4, 5])
>>> a.append(3)
>>> t
([1, 2, 3], [4, 5])

A tuple can also be nested, i.e. just like a list inside a tuple, we can have tuples inside a tuple.

>>> a = (1, 2)
>>> b = (4, 5)
>>> t = (a, b)
>>> t
((1, 2), (4, 5))

However, now that tuples are not mutable, we cannot update the tuple inside a tuple either.

If we really want to update a tuple, we can use that tuple to create another tuple.

>>> t2 = (t[0], (3), t[1])
>>> t2
((1, 2), 3, (4, 5))

Deleting a Tuple

Since tuples are immutable, it is not possible to delete individual elements of a tuple, however, we can delete the whole tuple itself.

>>> t = (1, "abc", 3.0)
>>> del t
>>> t # If we try to access the tuple after deleting it, python will raise an error
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 't' is not defined

Slicing a Tuple

Tuple slicing is similar to string slicing. Using slicing we can extract out elements of any tuple. We have to provide the starting index and the ending index i.e. tuple[start:end]

>>> t = ('s', 'u', 's', 'a', 'n')
>>> t[1:4]
('u', 's', 'a')

It starts from start and ends right before end. It won’t print the element at the index end. As in the example above, we have n at the 4th index of tuple t, however, it printed only till a.

If the start is out of the range of the tuple, then it prints empty tuple.

>>> t[5:7]
()

If you don’t provide start, then it will print from start till end-1 element.

>>> t[:3]
('s', 'u', 's')

Similarly, if end is not provided, it prints till the last element of the tuple.

>>> t[2:]
('s', 'a', 'n')

And if we don’t provide either of them? You guessed it right! It prints the whole tuple as is.

>>> t[:]
('s', 'u', 's', 'a', 'n')

Frequently used Tuple methods

Depending on the elements inside a tuple, there are certain useful methods we can use with a tuple.

>>> t = (5, 2, 9, 7)
>>> min(t) # Returns the minimum element
2
>>> max(t) # Returns the maximum element
9
>>> len(t) # Returns the length of the tuple
4

Using + to create a new tuple using existing tuples. This is called concatenation.

>>> t1 = (1, 2)
>>> t2 = (3,)
>>> t3 = (4, 5)
>>> t = (t1 + t2 + t3)
>>> t
(1, 2, 3, 4, 5)

In Python, you will notice so many similarities between the methods on strings, tuples and lists. It is so easy to understand them one you understand one of them. Next, we will see Lists in Python.


Note: This is a part of what I learned in an online Open Course Ware offered by MIT on edX. Its for my personal reference & also for those who would like to revisit the course.

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