什麼是可疊代物件？

Python 程式面試題實作練習

Kirill Smirnov

Data Science Consultant, Altran

定義

iterable objects / Iterables——能用於 for 迴圈的任何物件

list
tuple
set
dictionary
string

遍歷 list 或 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

遍歷 set

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

for battleship in battleships:
    print(battleship)

TIE Fighter
X-Wing Fighter
Millennium Falcon

遍歷字串

title = 'Star Wars'

for char in title:
    print(char)

S
t
a
r

W
a
r
s

遍歷 dictionary

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

取得鍵值對

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')

取得鍵值對

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'

較不直觀的物件：range

interval = range(0, 10)

print(interval)

range(0, 10)

for num in interval:
    print(num)

0
1
2
...
9

較不直觀的物件：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')

較不直觀的物件：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

可疊代物件作為參數

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

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

list(enumerate(villains))

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

可疊代物件作為參數

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')
}

如何知道我們處理的是可疊代物件

interval = range(0, 5)

interval_iter = iter(interval)

print(interval_iter)

<range_iterator object at 0x7f3bdf8ad300>

Iterator - an object knowing how to retrieve consecutive elements from an Iterable one by one

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

next(interval_iter)

next(interval_iter)

next(interval_iter)

StopIteration

描述 for 迴圈

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

描述 for 迴圈

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

許多可疊代物件都是迭代器

iter()
next()

e.g. 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() 或 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() 或 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]'>

消耗性可疊代物件

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

遍歷 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

直接遍歷

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

練習時間！

Python 程式面試題實作練習