Data Structures in Python: Lists and Tuples - Tuple

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According to its definition, "A tuple is a finite sequence (also known as an "ordered list") of objects, each of a specified type." In other words, a tuple is an ordered collection of objects of different types. In Python, a tuple is a list of comma-separated values but immutable, unlike a list. So the operations on a tuple are restricted to the ones that don't affect its immutability. Accordingly, the following are the operations that can be performed on a tuple:

1. Creation
2. Accessing

Due to a tuple's immutability, deletion and addition of new elements are not possible.

Creation: Creating or defining a tuple is as simple as giving a list of values within parenthesis. For example

>>> tup = (2, 4, 6, 8, 10)

is a tuple. If a tuple has only one element, it would be defined as follows:

>>> tup = (5,)

Accessing: Since lists and tuples are almost the same, the accessing mechanisms also work in a similar fashion. Elements of a tuple can be accessed in two ways:

• Index based: The elements of a tuple can be accessed using their indices. The index starts at 0. For example, to access an element at index 0 of a tuple tup, the statement would be:
  
  >>> tup = ('a', 'b', 'c', 'd', 'e')
  >>> tup[0]
  'a'
  
• Slicing: As with a list, slice operator can be used to access elements of a tuple. It selects a range of elements. For example the following statement selects elements between 1 and 3 (excluding 3):
  
  >>> tup[1:3]
  ('b', 'c')

That covers operations on a tuple. So the question arises, when do you use a list and when do you use a tuple? A list can be used in almost all cases. However, there are certain contexts where a tuple is more useful. These are:

• When you need speed. Tuples are faster than lists. If you're defining a constant set of values and all you're ever going to do with it is iterate through it, use a tuple instead of a list.
• When your data will not change. It makes your code safer if you "write-protect" data that does not need to be changed. Using a tuple instead of a list is like having an implied assert statement that this data is constant, and that special thought (and a specific function) is required to override that.

In all other contexts, lists can be used. That brings us to the next section, which is a real world example using a list.

Next: Lists and Tuples in the Real World >>
 

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