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Lists are one of the 4 data types in Python used to store collections of data. A short comparison of the containers is shown below:

Feature List Tuple Dictionary Set
Mutable (Can be modified in place) Yes No Yes (keys are immutable) Yes
Iterable (Can be use in for loop) Yes Yes Yes Yes
Ordered (Can access by index, slicing) Yes Yes No No
Duplicate Values Allowed Allowed Not in keys Not allowed

Lists

Getting values with indexes

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

>>> furniture[0]
# 'table'

>>> furniture[1]
# 'chair'

>>> furniture[2]
# 'rack'

>>> furniture[3]
# 'shelf'

Negative indexes

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

>>> furniture[-1]
# 'shelf'

>>> furniture[-3]
# 'chair'

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

Getting sublists with Slices

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

>>> furniture[0:4]
# ['table', 'chair', 'rack', 'shelf']

>>> furniture[1:3]
# ['chair', 'rack']

>>> furniture[0:-1]
# ['table', 'chair', 'rack']

>>> furniture[:2]
# ['table', 'chair']

>>> furniture[1:]
# ['chair', 'rack', 'shelf']

>>> furniture[:]
# ['table', 'chair', 'rack', 'shelf']

Slicing the complete list will perform a copy:

>>> spam2 = spam[:]
# ['cat', 'bat', 'rat', 'elephant']

>>> spam.append('dog')
>>> spam
# ['cat', 'bat', 'rat', 'elephant', 'dog']

>>> spam2
# ['cat', 'bat', 'rat', 'elephant']

Getting a list length with len()

>>> furniture = ['table', 'chair', 'rack', 'shelf']
>>> len(furniture)
# 4

Changing values with indexes

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

>>> furniture[0] = 'desk'
>>> furniture
# ['desk', 'chair', 'rack', 'shelf']

>>> furniture[2] = furniture[1]
>>> furniture
# ['desk', 'chair', 'chair', 'shelf']

>>> furniture[-1] = 'bed'
>>> furniture
# ['desk', 'chair', 'chair', 'bed']

Concatenation and Replication

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

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

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

Using for loops with Lists

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

>>> for item in furniture:
...     print(item)
# table
# chair
# rack
# shelf

Getting the index in a loop with enumerate()

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

>>> for index, item in enumerate(furniture):
...     print('index', index, '- item:', item)
# index: 0 - item: table
# index: 1 - item: chair
# index: 2 - item: rack
# index: 3 - item: shelf

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 table costs $100
# The chair costs $50
# The rack costs $80
# The shelf costs $40

The in and not in operators

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

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

>>> 'bed' not in furniture
# True

>>> 'rack' not in furniture
# False

The Multiple Assignment (Unpacking) 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
# 'table'

>>> chair
# 'chair'

>>> rack
# 'rack'

>>> shelf
# '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)
# chair

>>> print(b)
# table

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')
# 1

Adding Values

append()

append adds an element to the end of a list:

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

insert()

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

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

Removing Values

del

del removes an item using the index:

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

>>> del furniture[2]
>>> furniture
# ['table', 'chair']

remove()

remove removes an item with using actual value of it:

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

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If the value appears multiple times in the list, only the first instance of the value will be removed.

Sorting values with sort()

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

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

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

>>> furniture.sort(reverse=True)
>>> furniture
# ['table', 'shelf', 'rack', 'chair']

By default, string are sorted using ASCII order and 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
# ['a', 'A', 'z', 'Z']

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

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

Comprehension (Like the set-builder notation)

List Comprehensions are a special kind of syntax that let us create lists out of other lists, and are incredibly useful when dealing with numbers and with one or two levels of nested for loops.

This is how we create a new list from an existing collection with a For Loop:

>>> names = ['Charles', 'Susan', 'Patrick', 'George']

>>> new_list = []
>>> for n in names:
...     new_list.append(n)
...
>>> new_list
# ['Charles', 'Susan', 'Patrick', 'George']

And this is how we do the same with a List Comprehension:

>>> names = ['Charles', 'Susan', 'Patrick', 'George']

>>> new_list = [n for n in names]
>>> new_list
# ['Charles', 'Susan', 'Patrick', 'George']

We can do the same with numbers:

>>> n = [(a, b) for a in range(1, 3) for b in range(1, 3)]
>>> n
# [(1, 1), (1, 2), (2, 1), (2, 2)]

Adding conditionals

If we want new_list to have only the names that start with C, with a for loop, we would do it like this:

>>> names = ['Charles', 'Susan', 'Patrick', 'George', 'Carol']

>>> new_list = []
>>> for n in names:
...     if n.startswith('C'):
...         new_list.append(n)
...
>>> print(new_list)
# ['Charles', 'Carol']

In a List Comprehension, we add the if statement at the end:

>>> new_list = [n for n in names if n.startswith('C')]
>>> print(new_list)
# ['Charles', 'Carol']

To use an if-else statement in a List Comprehension:

>>> nums = [1, 2, 3, 4, 5, 6]
>>> new_list = [num*2 if num % 2 == 0 else num for num in nums]
>>> print(new_list)
# [1, 4, 3, 8, 5, 12]

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Note that most of the time method will modify list in place, while function will create a new list

Tuples

The Tuple data type

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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]
# 'table'

>>> furniture[1:3]
# ('chair', 'rack')

>>> len(furniture)
# 4

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])
# ('cat', 'dog', 5)

>>> list(('cat', 'dog', 5))
# ['cat', 'dog', 5]

>>> list('hello')
# ['h', 'e', 'l', 'l', 'o']