Co jsou iterovatelné objekty?

Procvičování otázek z kódovacích pohovorů v Pythonu

Kirill Smirnov

Data Science Consultant, Altran

Definice

iterovatelné objekty / Iterables – libovolný objekt použitelný v cyklu for

list
tuple
set
dictionary
string

Iterace přes list nebo tuple

list:

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

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

tuple:

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

for droid in droids:
    print(droid)

R2-D2
TC-16
C-3PO

Iterace přes množinu

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

for battleship in battleships:
    print(battleship)

TIE Fighter
X-Wing Fighter
Millennium Falcon

Iterace přes řetězec

title = 'Star Wars'

for char in title:
    print(char)

S
t
a
r

W
a
r
s

Iterace přes slovník

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

Získání párů klíč–hodnota

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')

Získání párů klíč–hodnota

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'

Méně viditelné objekty: range

interval = range(0, 10)

print(interval)

range(0, 10)

for num in interval:
    print(num)

0
1
2
...
9

Méně viditelné objekty: 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')

Méně viditelné objekty: 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(), atd.

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

list(enumerate(villains))

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

Iterables jako argumenty

list(), tuple(), set(), atd.

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

list(enumerate(villains))

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

set(enumerate(villains))

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

Jak zjistit, zda pracujeme s Iterable

interval = range(0, 5)

interval_iter = iter(interval)

print(interval_iter)

<range_iterator object at 0x7f3bdf8ad300>

Iterator – objekt, který umí postupně načítat prvky z Iterable jeden po druhém

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

Popis cyklu 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

Popis cyklu 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

Mnoho Iterables je zároveň Iterators

iter()
next()

např. enumerate, finditer atd.

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() nebo 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() nebo 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]'>

Jednorázové Iterables

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

Procházení 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

Přímý přístup

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!

Procvičování otázek z kódovacích pohovorů v Pythonu