Czym są obiekty iterowalne?

Ćwiczenie pytań na rozmowach kwalifikacyjnych z programowania w Pythonie

Kirill Smirnov

Data Science Consultant, Altran

Definicja

obiekty iterowalne / Iterables - każdy obiekt, który może być użyty w pętli for

lista
krotka
zbiór
słownik
łańcuch znaków

Iterowanie po liście lub krotce

lista:

droids = ['R2-D2', 'TC-16', 'C-3PO']

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

krotka:

droids = ('R2-D2', 'TC-16', 'C-3PO')

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

Iterowanie po zbiorze

battleships = {'X-Wing Fighter', 'Millennium Falcon', 'TIE Fighter'}

for battleship in battleships:
    print(battleship)

TIE Fighter
X-Wing Fighter
Millennium Falcon

Iterowanie po łańcuchu znaków

title = 'Star Wars'

for char in title:
    print(char)

S
t
a
r

W
a
r
s

Iterowanie po słowniku

episodes = {
    'Episode I': 'The Phantom Menace',
    'Episode II': 'Attack of the Clones',
    'Episode III': 'Revenge of the Sith', 
    'Episode IV': 'A New Hope',
    'Episode V': 'The Empire Strikes Back',
    'Episode VI': 'Return of the Jedi'
}

for episode in episodes:
    print(episode)

Episode I
Episode II
Episode III
Episode IV
Episode V
Episode VI

Pobieranie par klucz-wartość

episodes = {
    'Episode I': 'The Phantom Menace',
    'Episode II': 'Attack of the Clones',
    'Episode III': 'Revenge of the Sith', 
    'Episode IV': 'A New Hope',
    'Episode V': 'The Empire Strikes Back',
    'Episode VI': 'Return of the Jedi'
}

for item in episodes.items():
    print(item)

('Episode I', 'The Phantom Menace')
('Episode II', 'Attack of the Clones')
('Episode III', 'Revenge of the Sith')
('Episode IV', 'A New Hope')
('Episode V', 'The Empire Strikes Back')
('Episode VI', 'Return of the Jedi')

Pobieranie par klucz-wartość

episodes = {
    'Episode I': 'The Phantom Menace',
    'Episode II': 'Attack of the Clones',
    'Episode III': 'Revenge of the Sith', 
    'Episode IV': 'A New Hope',
    'Episode V': 'The Empire Strikes Back',
    'Episode VI': 'Return of the Jedi'
}

for title, subtitle in episodes.items():
    print(title + ': ' + subtitle)

'Episode I': 'The Phantom Menace'
'Episode II': 'Attack of the Clones'
'Episode III': 'Revenge of the Sith'
'Episode IV': 'A New Hope'
'Episode V': 'The Empire Strikes Back'
'Episode VI': 'Return of the Jedi'

Obiekty mniej wizualne: range

interval = range(0, 10)

print(interval)

range(0, 10)

for num in interval:
    print(num)

0
1
2
...
9

Obiekty mniej wizualne: enumerate

villains = ['Darth Maul', 'Palpatine', 'Darth Vader']
enum_villains = enumerate(villains)

for item in enum_villains:
    print(item)

(0, 'Darth Maul')
(1, 'Palpatine')
(2, 'Darth Vader')

Obiekty mniej wizualne: enumerate

villains = ['Darth Maul', 'Palpatine', 'Darth Vader']
enum_villains = enumerate(villains)

for idx, name in enum_villains:
    print(str(idx) + ' - ' + name)

0 - Darth Maul
1 - Palpatine
2 - Darth Vader

Iterables jako argumenty

list(), tuple(), set(), etc.

villains = [
    'Darth Maul',
    'Palpatine',
    'Darth Vader'
]

list(enumerate(villains))

[
    (0, 'Darth Maul'),
    (1, 'Palpatine'),
    (2, 'Darth Vader')
]

Iterables jako argumenty

list(), tuple(), set(), etc.

villains = [
    'Darth Maul',
    'Palpatine',
    'Darth Vader'
]

list(enumerate(villains))

[
    (0, 'Darth Maul'),
    ...

set(enumerate(villains))

{
    (0, 'Darth Maul'),
    (1, 'Palpatine'),
    (2, 'Darth Vader')
}

Jak rozpoznać obiekt iterowalny

interval = range(0, 5)

interval_iter = iter(interval)

print(interval_iter)

<range_iterator object at 0x7f3bdf8ad300>

Iterator - obiekt wiedzący, jak pobierać kolejne elementy z Iterable jeden po drugim

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

Opis pętli for

droids = ['R2-D2', 'TC-16', 'C-3PO']

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

iter_droids = iter(droids)

while True:
    try:


    except StopIteration:
        break

Opis pętli for

droids = ['R2-D2', 'TC-16', 'C-3PO']

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

iter_droids = iter(droids)

while True:
    try:
        droid = next(iter_droid)
        print(droid)
    except StopIteration:
        break

R2-D2
TC-16
C-3PO

Wiele Iterables to jednocześnie Iteratory

iter()
next()

np. enumerate, finditer etc.

import re
pattern = re.compile(r'[\w\.]+@[a-z]+\.[a-z]+')

text = '[email protected] is the e-mail of John. He often writes to his boss '\
'at [email protected]. But the messages get forwarded to his secretary at [email protected].'

result = re.finditer(pattern, text)

iter() lub next()

iter()

result = re.finditer(pattern, text)

for item in result:
    print(item)

<_sre.SRE_Match object; span=(0, 22), match='[email protected]'>
<_sre.SRE_Match object; span=(77, 93), match='[email protected]'>
<_sre.SRE_Match object; span=(146, 162), match='[email protected]'>

iter() lub next()

next()

result = re.finditer(pattern, text)

next(result)

<_sre.SRE_Match object; span=(0, 22),
match='[email protected]'>

next(result)

<_sre.SRE_Match object; span=(77, 93),
match='[email protected]'>

next(result)

<_sre.SRE_Match object; span=(146, 162),
match='[email protected]'>

Iterables jednorazowego użytku

result = re.finditer(pattern, text)
for item in result:
    print(item)

<_sre.SRE_Match object; ...
<_sre.SRE_Match object; ...
<_sre.SRE_Match object; ...

for item in result:
    print(item)

# nothing

short_list = [2, 4]
for item in short_list:
    print(item)

2
4

for item in short_list:
    print(item)

2
4

Przechodzenie przez DataFrame

pars = {'weight': [168, 183, 198], 'height': [77, 79, 135]}
characters = pd.DataFrame(pars, index=['Luke Skywalker', 'Han Solo', 'Darth Vader'])
print(characters)

                weight  height
Luke Skywalker     168      77
Han Solo           183      79
Darth Vader        198     135

Podejście bezpośrednie

for item in characters:
    print(item)

weight
height

.iterrows()

result = characters.iterrows()

print(result)

<generator object DataFrame.iterrows at 0x7f5dff6b9c50>

.iterrows()

result = characters.iterrows()

for item in result:
    print(item)

item $\rightarrow$ (index name, Series)

('Luke Skywalker',
weight    168
height     77
Name: Luke Skywalker, dtype: int64)
('Han Solo',
weight    183
height     79
Name: Han Solo, dtype: int64)
('Darth Vader',
weight    198
height    135
Name: Darth Vader, dtype: int64)

.iterrows()

result = characters.iterrows()

for index, series in result:
    print(index)
    print(series)

Luke Skywalker
weight    168
height     77
Name: Luke Skywalker, dtype: int64)
Han Solo
weight    183
height     79
Name: Han Solo, dtype: int64)
Darth Vader
weight    198
height    135
Name: Darth Vader, dtype: int64)

.iteritems()

result = characters.iteritems()

print(result)

<generator object DataFrame.iteritems at 0x7f5dff69f938>

.iteritems()

result = characters.iteritems()

for item in result:
    print(item)

item $\rightarrow$ (column name, Series)

('weight',
Luke Skywalker    168
Han Solo          183
Darth Vader       198
Name: weight, dtype: int64)
('height',
Luke Skywalker     77
Han Solo           79
Darth Vader       135
Name: height, dtype: int64)

.iteritems()

result = characters.iteritems()

for name, series in result:
    print(name)
    print(series)

weight
Luke Skywalker    168
Han Solo          183
Darth Vader       198
Name: weight, dtype: int64
height
Luke Skywalker     77
Han Solo           79
Darth Vader       135
Name: height, dtype: int64

Lass uns üben!

Ćwiczenie pytań na rozmowach kwalifikacyjnych z programowania w Pythonie