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Chapter4-Lists.md

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4 Lists

List data type

List value that contains multiple values
The values is also called items
Comma-delimited
You can access items in a list with it's integer index
The index start from 0
You can use negative indexes, -1: the last
You can get multiple items using slices
The slice has 2 indexes, start from the first index, but not include the last
len() function, concatenation and replication
You can convert a value into a list

>>> lili = ['cat', 'dog', 'mouse']
>>> lili
['cat', 'dog', 'mouse']
>>> lili[0]
'cat'
>>>

List can contain lists:

>>> lolo = [['carrot', 'spinach'],[1,2,3]]
>>> lolo [0]
['carrot', 'spinach']
>>> lolo[1][1]
2

Negative indexes:

>>> lili = ['cat', 'dog', 'snake', 'bird', 'mouse']
>>> lili[-1]
'mouse'

Sublist with Slices

slice (from x to y , but not include y)

>>> lili = ['cat', 'dog', 'snake', 'bird', 'mouse']
>>> lili[1:3]
['dog', 'snake']

index: single item slice: list of values

Changing value:

>>> lili = ['cat', 'dog', 'snake', 'bird', 'mouse']
>>> lili[2:4] = ['TIGER', 'ELEPHANT', 'RHINO']
>>> lili
['cat', 'dog', 'TIGER', 'ELEPHANT', 'RHINO', 'mouse']

Slice shortcut

>>> lili = ['cat', 'dog', 'snake', 'bird', 'mouse']
>>> lili[:2]
['cat', 'dog']
>>> lili[2:]
['snake', 'bird', 'mouse']

Delete from the list:

>>> lili = ['cat', 'dog', 'snake', 'bird', 'mouse']
>>> del lili[2]
>>> lili
['cat', 'dog', 'bird', 'mouse']

del = unassignment statement

You can mix:

>>> cooco = ['lala', 1, 3, 'oops']
>>> cooco
['lala', 1, 3, 'oops']

List length:

>>> len('hello')
5
>>> len([1,2,3])
3

Concatenation

>>> 'hello ' + 'word'
'hello word'
>>> [1,2,3] + [4,5,6]
[1, 2, 3, 4, 5, 6]

>>> 'hello'*3
'hellohellohello'
>>> [1,2,3]*3
[1, 2, 3, 1, 2, 3, 1, 2, 3]

tl;dr: string = list of single characters values

list() function

>>> int('33')
33
>>> str(33)
'33'
>>> list('hello')
['h', 'e', 'l', 'l', 'o']

in and not operators

to check if the value is in or not in the list

>>> 'heiya' in ['hello', 'hij', 'chao', 'heiya']
True

>>> 'hoy' in ['hello', 'hij', 'chao', 'heiya']
False

>>> 'heiya' not in ['hello', 'hij', 'chao', 'heiya']
False
```python

### For Loops with List

for loops technically iterates over the values in a list
```python
>>> for i in range(4):
	print(i)
0
1
2
3

this is similar to

>>> range(4)
range(0, 4)
>>> [0,1,2,3]
[0, 1, 2, 3]

range() function returns a list-like value, which can be passed to the list() function if you need an actual list value

>>> for i in [0, 1, 2, 3]:
	print(i)
0
1
2
3

list like ~ sequence

>>> list(range(4))
[0, 1, 2, 3]

>>> list(range(0, 100, 2))
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98]

>>> lolo  =  list(range(0, 100, 2))
>>> lolo
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98]

for i in range(len(someList)):

>>> for i in range(len(supplies)):
	print('Index '  + str(i) + ' in supplies is: ' + supplies[i])
Index 0 in supplies is: pens
Index 1 in supplies is: staples
Index 2 in supplies is: paper
Index 3 in supplies is: bin

Multiple Assignment

>>> cat = ['fat', 'orange', 'loud']
>>> size = cat[0]
>>> color = cat[1]
>>> disposition = cat[2]
>>> 
>>> # the same as
>>> size, color, disposition = cat
>>> size
'fat'
>>> color
'orange'
>>> 
>>> size, color, disposition = 'skinny', 'black' , 'quiet'
>>> color
'black'

Swapping Variables

Variables can swap their values using multiple assignment

>>> a = 'AAA'
>>> b = 'BBB'
>>> a,b = b,a
>>> a
'BBB'
>>> b
'AAA'

Augmented Assignment Operators (shortcuts)

>>> lolo = 33
>>> lolo = lolo + 1
>>> lolo
34
>>> ## same as
>>> lolo = 33
>>> lolo += 1
>>> lolo
34

lolo += 1  | lolo = lolo + 1
lolo -= 1   | lolo = lolo - 1
lolo /= 1   | lolo = lolo / 1
lolo %= 1    | lolo = lolo % 1

Methods

Methods are function that are "called on" values

index() : returns the index of an item in the list

>>> lolo = ['hi', 'hello', 'heiya']
>>> lolo.index('hello')
1

If there is a duplicate only shows the first match:

>>> lolo = ['hi', 'hello', 'heiya', 'heiya']
>>> lolo.index('heiya')
2

append() : adds a value anywhere inside the list

>>> animal = ['cat', 'dog', 'mouse']
>>> animal.append('snake')
>>> animal
['cat', 'dog', 'mouse', 'snake']

insert()

>>> animal = ['cat', 'dog', 'mouse']
>>> animal.insert(1, 'snake')
>>> animal
['cat', 'snake', 'dog', 'mouse']

remove()

>>> animal = ['cat', 'dog', 'mouse']
>>> animal.remove('dog')
>>> animal
['cat', 'mouse']

removed() only remove the first found element:

animal = ['cat', 'dog', 'mouse', 'cat', 'cat', 'cat']
>>> animal = ['cat', 'dog', 'mouse', 'cat', 'cat', 'cat']
>>> animal.remove('cat')
>>> animal
['dog', 'mouse', 'cat', 'cat', 'cat']

del (similar to remove())

>>> animal = ['cat', 'dog', 'mouse']
>>> del animal[0]
>>> animal
['dog', 'mouse']

sort()

>>> lolo = [ 1, 5, 22, 88, -34]
>>> lolo.sort()
>>> lolo
[-34, 1, 5, 22, 88]

>>> animal = ['cat', 'dog', 'mouse', 'cat', 'cat', 'cat']
>>> animal.sort()
>>> animal
['cat', 'cat', 'cat', 'cat', 'dog', 'mouse']
>>> animal.sort(reverse=True)
>>> animal
['mouse', 'dog', 'cat', 'cat', 'cat', 'cat']

It's ASCII-betical

>>> animal = ['Cat', 'Dog', 'mouse', 'ant', 'bird']
>>> animal.sort()
>>> animal
['Cat', 'Dog', 'ant', 'bird', 'mouse']
>>> animal.sort(key=str.lower)
>>> animal
['ant', 'bird', 'Cat', 'Dog', 'mouse']

Mutable VS Immutable data type

String and list are similar, but strings are immutable.

Many things that we can do with list can be done with string

>>> list('hello')
['h', 'e', 'l', 'l', 'o']
>>> name = 'Macarana'
>>> name[0]
'M'
>>> name[-2]
'n'
>>> 'ca' in name
True
>>> 'co' in name
False
>>> for letter in name:
	print(letter)
M
a
c
a
r
a
n
a

BUT list is mutable data type
string is immutable data type
tuple is also immutable

Mutable values like lists can be modified in place.

Immutable values like strings and tuples cannot be modified "in place", hence it does not use reference.

To edit the string:

>>> title = 'Pussy a cat'
>>> newTitle = title[0:6] + 'the ' + title[8:12]
>>> newTitle
'Pussy  the cat'

The difference between immutable and mutable comes up with "references"

mutable: uses reference (ex: list)
immutable: does not user reference (ex: string)

variable store value like below, copy whatever value from one variable to another:

>>> lolo = 33
>>> lili = lolo
>>> lili = 22
>>> lili
22
>>> lolo
33

But list don’t work quite the same, when we assign a list, we assign a list variable:

>>> roro = [0,1,2,3]
>>> riri = roro
>>> riri[1] = 'hello'
>>> riri
[0, 'hello', 2, 3]
>>> roro
[0, 'hello', 2, 3]

We're assigning a reference to riri

Variables don't contain lists, they contain references to lists.

When passing a list argument to a function, you are actually passing a list reference.

def eggs(someParameter):
    someParameter.append('hello')
spam = [1, 2, 3]
eggs(spam)
print(spam)

# OUTPUT:
[1, 2, 3, 'hello']

Note: the added value should have been local variable, but not for the case of reference

Changes made to a list in a function will affect the list outside the function.

copy()

>>> import copy
>>> animal = ['cat', 'dog', 'mouse']
>>> living = copy.deepcopy(animal)
>>> living[1] = 'croc'
>>> animal
['cat', 'dog', 'mouse']
>>> living
['cat', 'croc', 'mouse']

Multiple lines:

>>> animal= [ 'cat',
	      'dog',
	      'bird']
>>> animal
['cat', 'dog', 'bird']

or use \ line continuation character to stretch Python instruction across multiple lines.

>>> print ('at this moment ' + \
       'you should be...')
at this moment you should be...