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Getting values with indexes

Getting values with indexes

title: Python Lists and Tuples description: In python, Lists are are one of the 4 data types in Python used to store collections of data.

Python Lists

Lists are one of the 4 data types in Python used to store collections of data.

['John', 'Peter', 'Debora', 'Charles']

Getting values with indexes 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> furniture[0]

>>> furniture[1]

>>> furniture[2]

>>> furniture[3]

Negative indexes 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> furniture[-1]

>>> furniture[-3]

>>> f'The {furniture[-1]} is bigger than the {furniture[-3]}'

Getting sublists with Slices 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> furniture[0:4]

>>> furniture[1:3]

>>> furniture[0:-1]

>>> furniture[:2]

>>> furniture[1:]

>>> furniture[:]

Slicing the complete list will perform a copy:

>>> spam2 = spam[:]

>>> spam.append('dog')
>>> spam

>>> spam2

Getting a list length with len() 

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> len(furniture)

Changing values with indexes 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> furniture[0] = 'desk'
>>> furniture

>>> furniture[2] = furniture[1]
>>> furniture

>>> furniture[-1] = 'bed'
>>> furniture

Concatenation and Replication 

>>> [1, 2, 3] + ['A', 'B', 'C']

>>> ['X', 'Y', 'Z'] * 3

>>> my_list = [1, 2, 3]
>>> my_list = my_list + ['A', 'B', 'C']
>>> my_list

Using for loops with Lists 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> for item in furniture:
...     print(item)

Getting the index in a loop with enumerate() 

>>> furniture = ['table', 'chair', 'rack', 'shelf']

>>> for index, item in enumerate(furniture):
...     print(f'index: {index} - item: {item}')

Loop in Multiple Lists with zip() 

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> price = [100, 50, 80, 40]

>>> for item, amount in zip(furniture, price):
...     print(f'The {item} costs ${amount}')

The in and not in operators 

>>> 'rack' in ['table', 'chair', 'rack', 'shelf']

>>> 'bed' in ['table', 'chair', 'rack', 'shelf']

>>> 'bed' not in furniture

>>> 'rack' not in furniture

The Multiple Assignment Trick

The multiple assignment trick is a shortcut that lets you assign multiple variables with the values in a list in one line of code. So instead of doing this:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> table = furniture[0]
>>> chair = furniture[1]
>>> rack = furniture[2]
>>> shelf = furniture[3]

You could type this line of code:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> table, chair, rack, shelf = furniture

>>> table

>>> chair

>>> rack

>>> shelf

The multiple assignment trick can also be used to swap the values in two variables:

>>> a, b = 'table', 'chair'
>>> a, b = b, a
>>> print(a)

>>> print(b)

The index Method

The index method allows you to find the index of a value by passing its name:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> furniture.index('chair')

Adding Values

append()

append adds an element to the end of a list:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> furniture.append('bed')
>>> furniture

insert()

insert adds an element to a list at a given position:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> furniture.insert(1, 'bed')
>>> furniture

Removing Values

del()

del removes an item using the index:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> del furniture[2]
>>> furniture

>>> del furniture[2]
>>> furniture

remove()

remove removes an item with using actual value of it:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> furniture.remove('chair')
>>> furniture
Removing repeated items If the value appears multiple times in the list, only the first instance of the value will be removed.

pop()

By default, pop will remove and return the last item of the list. You can also pass the index of the element as an optional parameter:

>>> animals = ['cat', 'bat', 'rat', 'elephant']

>>> animals.pop()
'elephant'

>>> animals
['cat', 'bat', 'rat']

>>> animals.pop(0)
'cat'

>>> animals
['bat', 'rat']

Sorting values with sort() 

>>> numbers = [2, 5, 3.14, 1, -7]
>>> numbers.sort()
>>> numbers

furniture = ['table', 'chair', 'rack', 'shelf']
furniture.sort()
furniture

You can also pass True for the reverse keyword argument to have sort() sort the values in reverse order:

>>> furniture.sort(reverse=True)
>>> furniture

If you need to sort the values in regular alphabetical order, pass str.lower for the key keyword argument in the sort() method call:

>>> letters = ['a', 'z', 'A', 'Z']
>>> letters.sort(key=str.lower)
>>> letters

You can use the built-in function sorted to return a new list:

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> sorted(furniture)

The Tuple data type

Tuples vs Lists The key difference between tuples and lists is that, while tuples are immutable objects, lists are mutable. This means that tuples cannot be changed while the lists can be modified. Tuples are more memory efficient than the lists. 
>>> furniture = ('table', 'chair', 'rack', 'shelf')

>>> furniture[0]

>>> furniture[1:3]

>>> len(furniture)

The main way that tuples are different from lists is that tuples, like strings, are immutable.

Converting between list() and tuple() 

>>> tuple(['cat', 'dog', 5])

>>> list(('cat', 'dog', 5))

>>> list('hello')
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