Introduction to Machine Learning

You can add new items to the end of the list by using its append() method (list is an object!)

>>> numbers = []          # this creates a new empty list
>>> numbers.append(6)
>>> print(numbers)
>>> numbers.append(2)
>>> print(numbers)

>>> numbers = [1, 2, 3]
>>> numbers.extend([4, 5, 6])
>>> print(numbers)

>>> numbers = [1, 2, 3]
>>> print(numbers)
>>> del numbers[1]
>>> print(numbers)

The official documentation provides many more methods for the list object, for example .extend(), .insert(), .pop(), .remove(), .reverse(), .index(), and .sort(). Please explore these at your own leisure.

List operators

The operators + and * have been overloaded for lists.

So, you can concatenate two lists by ‘adding’ the list together. Try this and see what happens.

>>> print([1, 2] + [3, 4, 5])

You can also replicate elements in a list by ‘mutiplying’ it with a scalar. Try this and see what happens.

>>> print([1, 2] * 3)

The membership operator (in) is also useful for checking whether a particular object is in a list. This returns a bool (True or False).

>>> print(3 in [1,2,3,4])
>>> print(3 not in [1,2,3,4])
>>> print("snake" in ["I", "am", "not", "afraid", "of", "Python"])