Introduction to Machine Learning

Python also provides another sequence type called tuples.

Tuples are like lists. The main difference is that lists are mutable (can be modified), while tuples are immutable (cannot be changed).

So you cannot add/remove items to/from a tuple once you have created it.

Tuples are useful for representing ordered, fixed-size grouping of elements, like 2D coordinates \((x, y)\) or 3D coordinates \((x, y, z)\).

Creating a new tuple is just like creating a list, except that you use (parenthesis) instead of [square brackets].

>>> my_vector = (1, 3, 4)
>>> print(my_vector)

You can also convert an existing list (or any Python sequence type) into a new tuple object.

>>> my_list = [1, 3, 4]
>>> my_vector = tuple(my_list)
>>> print(my_vector)

You can use tuples just like you would use lists:

>>> x = (1, 2, 3, 4, 5)
>>> print(x[0])
>>> print(x[1:3])
>>> print(x[-1])
>>> print(x[:4:2])
>>> print(x[::-1])

… except that you cannot modify the elements. Try the following, and understand the error messages produced by Python.

>>> x[1] = 6      # Python will complain!
>>> x.append(6)   # ... and complain again!

>>> non_tuple = (1)
>>> print(non_tuple)
>>> print(type(non_tuple))
>>> singleton = (1, )
>>> print(singleton)
>>> print(type(singleton))