2-types.md

Types in Depth

[ Amit Kotlovski ](mailto:amit@amitkot.com) / [ @amitkot ](http://twitter.com/amitkot)

Agenda

Numbers
Strings
Tuples
Lists
Sets
Dictionaries

Numbers

int
float
long
complex

Numbers

int is implemented as C long (32 bits at least)
long is unlimited
float is implemented as C double

`int` bases

Binary (0b prefix)
Octal (0o prefix)
Decimal (no prefix)
Hexadecimal (0x prefix)

`int` division

print(12 / 5)
⇒ 2				// only whole part
print(12.0 / 5)
⇒ 2.4			// exact
print(12 / 5.0)
⇒ 2.4			// exact

Converting Types

>>> int(12.567)
12

>>> float(12)
12.0

>>> str(12.0)
'12.0'

Strings

'this is a string'
"this is also a string"
"""This is a long string that may span more than one line but still stay one string"""
'these strings are now ' + 'concatenated together'
converting other types to string using str()

Tuples

Features

Holds a sequence of items
Similar to list but immutable

Creating a tuple

From scratch

>>> t1 = (1, 2, 3)
>>> t1
(1, 2, 3)
>>> t2 = (1,)
>>> t2
(1,)
>>> t3 = 1,
>>> t3
(1,)

Creating a tuple

Converting a list

>>> a = [1, 2, 3]
>>> tuple(a)
(1, 2, 3)

Immutable Container

Once created, a tuple does not change:

>>> t = (1, 2, 3)
>>> t
(1, 2, 3)
>>> t.add(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'add'

Immutable Container

Keeping a mutable object inside a tuple allows mutations of that object

>>> a = [1, 2, 3]
>>> t = ('first', a, 'last')
>>> t
('first', [1, 2, 3], 'last')
>>> t[1].append('banana')
>>> t
('first', [1, 2, 3, 'banana'], 'last')

Slicing

Accessing a single item

# third index
>>> t = ('Atreides', 'Ordos', 'Harkonnen')
>>> t[2]
'Harkonnen'

# last index
>>> t[-1]
'Harkonnen'

Slicing

Slicing a range

>>> t = ('Atreides', 'Ordos', 'Harkonnen')
>>> t[0:2]
('Atreides', 'Ordos')

Slicing - Full syntax

slice = tuple_name[start:end:step]

Parameter	Description
`start`	first index of the slice
`end`	the index after the last index of the slice
`step`	the step to take between each item in the slice

Example - Slicing a range with a step of 2

>>> t = (0, 1, 2, 3, 4, 5, 6, 7, 8)
>>> t[2:8:2]
(2, 4, 6)

Slicing - Quiz

How will we slice backwards from the item at location 8 until the item at location 2 with a step of 2?

>>> t = (0, 1, 2, 3, 4, 5, 6, 7, 8)

Useful Operations

Packing and Unpacking
Swapping
Adding
Multiplying
Length

Packing and Unpacking

Packing

>>> a = 1
>>> b = 2
>>> c = 3
>>> t = a, b, c

Unpacking

>>> t = (5, 6, 7)
>>> a, b, c = t
>>> print(a, b, c)
5 6 7

Swapping

How would you swap values between two variables?

Swapping - Using a Temporary variable

>>> a = 5
>>> b = 500
>>> print(a, b)
5 500
>>> temp = a
>>> a = b
>>> b = temp
>>> print(a, b)
500 5

Swapping - Using Tuples

>>> a = 33
>>> b = 111
>>> print(a, b)
33 111
>>> a, b = b, a     # Packing and Unpacking
>>> print(a, b)
111 33

Adding

Adding tuples concatenates them

>>> t1 = ('a', 'b')
>>> t2 = (99, 256)
>>> t1 + t2
('a', 'b', 99, 256)

Multiplying

Multiplying tuples is adding them to themselves

>>> t = ('a', 'b')
>>> 3 * t
('a', 'b', 'a', 'b', 'a', 'b')
>>> t * 3
('a', 'b', 'a', 'b', 'a', 'b')

Length

Using the len() function we previously met

>>> t1 = ('a', 'b')
>>> t2 = (99, 256)
>>> len(t1 + t2)
4

Questions

Lists

Adding to List

Appending to end of list

>>> simpsons = ['Homer', 'Marge', 'Lisa', 'Maggie']
>>> simpsons.append("Santa's Little Helper")
>>> simpsons
['Homer', 'Marge', 'Lisa', 'Maggie', "Santa's Little Helper"]

Adding to List

Inserting before a specific position

>>> simpsons
['Homer', 'Marge', 'Lisa', 'Maggie', "Santa's Little Helper"]
>>> simpsons.insert(2, 'Bart')
>>> simpsons
['Homer', 'Marge', 'Bart', 'Lisa', 'Maggie', \
 "Santa's Little Helper"]

Adding to List

Example: Inserting at the beginning of the list

>>> simpsons.insert(0, 'Abraham')
>>> simpsons
['Abraham', 'Homer', 'Marge', 'Bart', 'Lisa', 'Maggie', \
 "Santa's Little Helper"]

Remove

by Position

Default index is last item:

>>> simpsons
['Abraham', 'Homer', 'Marge', 'Bart', 'Lisa', 'Maggie', \
 "Santa's Little Helper"]
>>> person = simpsons.pop()     # pop last item
>>> person
"Santa's Little Helper"
>>> simpsons
['Abraham', 'Homer', 'Marge', 'Bart', 'Lisa', 'Maggie']

Specifying index for pop:

>>> person = simpsons.pop(0)    # pop at a specified index
>>> person
'Abraham'
>>> simpsons
['Homer', 'Marge', 'Bart', 'Lisa', 'Maggie']

Remove

by Content

>>> simpsons
['Homer', 'Marge', 'Bart', 'Lisa', 'Maggie']
>>> simpsons.remove('Lisa')
>>> simpsons
['Homer', 'Marge', 'Bart', 'Maggie']

It removes only the first occurrence:

>>> cats = ['Snowball', 'Snowball II', 'Snowball III', \
            'Coltrane', 'Snowball II']
>>> cats.remove('Snowball II')
>>> cats
['Snowball', 'Snowball III', 'Coltrane', 'Snowball II']

Sort

In Place

Strings:

>>> baratheon = ['Robert', 'Stannis', 'Renly']
>>> baratheon.sort()
>>> baratheon
['Renly', 'Robert', 'Stannis']

Numbers:

>>> numbers = [20, 500, 1, 17.3]
>>> numbers.sort()
>>> numbers
[1, 17.3, 20, 500]

Reverse Sort:

>>> numbers = [20, 500, 1, 17.3]
>>> numbers.sort(reverse=True)
>>> numbers
[500, 20, 17.3, 1]

Sort

Mixing different types?

mixed = [1, '2', [3, 4]]

Can we run mixed.sort()?

##Python 2 - _Yeah, OK_

##Python 3 - Nope

Sort

Not In Place

>>> numbers = [20, 500, 1, 17.3]
>>> sorted_numbers = sorted(numbers)
>>> numbers         # did not change
[20, 500, 1, 17.3]
>>> sorted_numbers  # sorted
[1, 17.3, 20, 500]

List Methods

Clear The List

>>> numbers = [20, 500, 1, 17.3]
>>> numbers.clear()
>>> numbers
[]

Counting Occurrences

>>> numbers = [20, 500, 1, 17.3, 20]
>>> numbers.count(20)
2

Extending The List

>>> numbers = [20, 500, 1, 17.3]
>>> more_numbers = [999, 888, 777]
>>> numbers.extend(more_numbers)
>>> numbers
[20, 500, 1, 17.3, 999, 888, 777]

Can also be achieved using +:

>>> numbers = [20, 500, 1, 17.3]
>>> more_numbers = [999, 888, 777]

>>> numbers + more_numbers
[20, 500, 1, 17.3, 999, 888, 777]

Finding An Item's Index

>>> numbers = [20, 500, 1, 17.3, 6, 17.3]
>>> numbers.index(17.3)
3

Reversing the List's Order

>>> numbers = [20, 500, 1, 17.3]
>>> numbers.reverse()
>>> numbers
[17.3, 1, 500, 20]

Questions

Sets

Basics

Creating a new Set

>>> s = {'once', 'once', (1, 2), 5.17}
>>> s
{(1, 2), 'once', 5.17}

Creating a Set from a List

>>> l = ['once', 'once', (1, 2), 5.17]
>>> l
['once', 'once', (1, 2), 5.17]
>>> s = set(l)
>>> s
{'once', (1, 2), 5.17}

Adding an item

>>> s
{'once', (1, 2), 5.17}
>>> s.add('banana')
>>> s
{'once', (1, 2), 5.17, 'banana'}

Removing an Item

>>> s
{'once', (1, 2), 5.17, 'banana'}
>>> s.remove('banana')
>>> s
{'once', (1, 2), 5.17}

Set Uses

Remove Duplicate Items in List

>>> l = ['first', 'second', 'second', 'second', 'third']
>>> set(l)
{'second', 'first', 'third'}

Intersection

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> yellow = {'mustard', 'lemon', 'banana', 'mango'}
>>> sweet.intersection(yellow)
{'mango', 'banana'}
>>> sweet & yellow              # short syntax
{'mango', 'banana'}

Union

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> yellow = {'mustard', 'lemon', 'banana', 'mango'}
>>> sweet.union(yellow)
{'mustard', 'banana', 'jam', 'sugar', 'lemon', 'mango'}
>>> sweet | yellow              # short syntax
{'mustard', 'banana', 'jam', 'sugar', 'lemon', 'mango'}

Difference

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> yellow = {'mustard', 'lemon', 'banana', 'mango'}
>>> sweet.difference(yellow)
{'sugar', 'jam'}
>>> sweet - yellow              # short syntax
{'sugar', 'jam'}

Symmetric Difference

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> yellow = {'mustard', 'lemon', 'banana', 'mango'}
>>> sweet.symmetric_difference(yellow)
{'jam', 'sugar', 'mustard', 'lemon'}
>>> sweet ^ yellow              # short syntax
{'jam', 'sugar', 'mustard', 'lemon'}

Subset\Superset

$Subset\Superset$

>>> yellow_fruits = {'banana', 'mango'}                 # A
>>> yellow = {'mustard', 'lemon', 'banana', 'mango'}    # B
>>> yellow_fruits.issubset(yellow)
True
>>> yellow_fruits < yellow      # short syntax
True

>>> yellow.issuperset(yellow_fruits)
True
>>> yellow > yellow_fruits      # short syntax
True

Disjoint

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> cars = {'Toyota', 'Mazda', 'Ford'}
>>> sweet.isdisjoint(cars)
True

Set Operations

`copy()`

Copies the Set to a new separate one

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> tastes = sweet.copy()
>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> has_taste = sweet.copy()
>>> has_taste.add('lemon')              # add to _new_ Set
>>> has_taste
{'mango', 'banana', 'sugar', 'jam', 'lemon'}
>>> sweet                               # did not change
{'jam', 'mango', 'sugar', 'banana'}

`discard()`

Removes an item from the Set, if it's there. Does not report error if not there.

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> sweet.discard('sugar')          # removes 'sugar'
>>> sweet.discard('watermelon')     # item not in Set, ignores the error
>>> sweet
{'jam', 'mango', 'banana'}

`pop()`

Extracts some item from the Set

>>> sweet = {'sugar', 'banana', 'mango', 'jam'}
>>> sweet.pop()
'mango'

`clear()`

Remove all items from the Set

>>> sweet = {'jam', 'sugar', 'banana', 'mango'}
>>> sweet.clear()
>>> sweet
set()

Questions

Dictionaries

Dictionary Creation

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> d
{'Bill': 'blue', 'David': 'brown', 'Ron': 'black'}

Equivalent to:

>>> e = dict()
>>> e['David'] = 'brown'
>>> e['Ron'] = 'black'
>>> e['Bill'] = 'blue'
>>> e
{'Bill': 'blue', 'David': 'brown', 'Ron': 'black'}

Keys & Values

Key - immutable

number
string
tuple

Value - Any Type

immutable types
lists
sets
dictionaries
user-created types (we'll soon meet)

Quiz

What will this dictionary contain?

>>> d = {'first': 'drink', 'first': 'eat'}

Adding, Getting and Removing

Adding

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> eye['Daenerys'] = 'violet'
>>> eye
{'Bill': 'blue', 'David': 'brown', 'Daenerys': 'violet', 
 'Ron': 'black'}

Get Value by Key

Method	Returns
d[key]	value for key, error if does not exist
get(key, default_val)	value for key if exists, default_val otherwise

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> eye['Ron']
'black'
>>> eye.get('Ron')
'black'
>>> eye.get('Owen', 'gold')     # Providing default value
'gold'

Remove - `del`

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> del eye['David']
>>> eye
{'Bill': 'blue', 'Ron': 'black'}

Remove - `pop()`

Extract an item, return it and remove it from the Dictionary:

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> bill_eye = eye.pop('Bill')
>>> bill_eye
'blue'
>>> eye
{'David': 'brown', 'Ron': 'black'}

Providing a default value, in case the key does not exist:

>>> eye.pop('George', 'green')
'green'
>>> eye
{'David': 'brown', 'Ron': 'black'}

Remove - `popitem()`

Pop some item from the Dictionary:

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> eye.popitem()
('Bill', 'blue')

Dictionary Methods

is Key in Dictionary?

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> 'Ron' in eye
True
>>> 'Jon' not in eye
True

`clear()`

>>> eye
{'Bill': 'blue', 'David': 'brown', 'Ron': 'black'}
>>> eye.clear()
>>> eye
{}

`copy()`

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> eye_same = eye
>>> eye_backup = eye.copy()
>>> eye['David'] = 'RED'
>>> eye
{'Bill': 'blue', 'David': 'RED', 'Ron': 'black'}
>>> eye_same
{'Bill': 'blue', 'David': 'RED', 'Ron': 'black'}
>>> eye_backup
{'Bill': 'blue', 'David': 'brown', 'Ron': 'black'}

`keys()`, `values()` and `items()`

A direct connection to the actual keys, values and items:

>>> eye = {'David': 'brown', 'Ron': 'black', 'Bill': 'blue'}
>>> k = eye.keys()
>>> v = eye.values()
>>> i = eye.items()

Changes to the dictionary affect them:

>>> eye['Sarah'] = 'green'
>>> k
dict_keys(['Bill', 'David', 'Sarah', 'Ron'])
>>> v
dict_values(['blue', 'brown', 'green', 'black'])
>>> i
dict_items([('Bill', 'blue'), ('David', 'brown'), 
            ('Sarah', 'green'), ('Ron', 'black')])

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Types in Depth

Agenda

Numbers

Numbers

int bases

int division

Converting Types

Strings

Tuples

Features

Creating a tuple

From scratch

Creating a tuple

Converting a list

Immutable Container

Immutable Container

Slicing

Slicing

Slicing - Full syntax

Slicing - Quiz

Useful Operations

Packing and Unpacking

Swapping

Swapping - Using a Temporary variable

Swapping - Using Tuples

Adding

Multiplying

Length

Questions

Lists

Adding to List

Appending to end of list

Adding to List

Inserting before a specific position

Adding to List

Example: Inserting at the beginning of the list

Remove

by Position

Remove

by Content

Sort

In Place

Sort

Mixing different types?

Sort

Not In Place

List Methods

Clear The List

Counting Occurrences

Extending The List

Finding An Item's Index

Reversing the List's Order

Questions

Sets

Basics

Creating a new Set

Creating a Set from a List

Adding an item

Removing an Item

Set Uses

Remove Duplicate Items in List

Intersection

Union

Difference

Symmetric Difference

Subset\Superset

Disjoint

Set Operations

copy()

discard()

pop()

clear()

Questions

Dictionaries

`int` bases

`int` division

`copy()`

`discard()`

`pop()`

`clear()`

Remove - `del`

Remove - `pop()`

Remove - `popitem()`

`clear()`

`copy()`

`keys()`, `values()` and `items()`