[python 기초] python의 list에 대하여

데이터 구조

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데이터를 일정한 기준(규칙)에 의해 모아 놓은 것

collection of data elements, structured in some way

- built-in + 확장

- Container type의 데이터 구조

1) Sequence = mapping by element position (index) 

ex) List, String

2) mapping = mapping by element name (key) 

ex) Dictionary

built-in Sequence (내장)

1) List

2) Tuple

3) String

4) Buffer objects

5) Xrange objects

Sequence에 대한 주요 작업

1) Indexing: 위치 [0 1 2]

2) Slicing: 범위 지정해서 추출

3) Adding: seq1 + seq2

4) Multiplying: seq1*5 (seq1 5번 반복)

5) Membership: 존재 여부 확인

List

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특징: Mutable!(변경가능)

- Indexing

- Slicing

- Adding, Multiplying, membership

- List methods

1) Method = object에 관련함수

Class -> object Instance

2) object.method(arguments)

1. Indexing

[index1:index2] ; index1=inclusive vs. index2=exclusive

간단한 예제)

(1) index번호는 0부터 시작하기 때문에 정확한 index값을 얻기 위해서는 (month -1)/(day-1) 을 해주어야 한다.

(2) endings: 1(st), 2(nd), 3(rd), 4~20(th) , 21(st), 22(nd), 23(rd), 24~30(th), 31(st)

months = ['Jan','Feb','Mar', 'Apr', 'May', 'Jun', 
          'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
 
#A list with one ending for each number from 1 to 31
endings = ['st', 'nd', 'rd'] + 17 * ['th'] \
        + ['st', 'nd', 'rd'] + 7 * ['th'] + ['st']
        
year = input('Year: ')
month = input('Month (1-12): ')
day = input('Day (1-31): ')
 
month_number = int(month)
day_number = int(day)
 
# Remember to subtract 1 from month and day to get a correct index
month_name = months[month_number-1]
ordinal = day + endings[day_number-1]
 
print("{}/{}, {}".format(month_name,ordinal,year))
# Year: 2015
# Month (1-12): 1
# Day (1-31): 31
# Jan/31st, 2015

2. slicing

tag = '<a herf="http://www.python.org">Python web site</a>'
 
print(tag[9:30]) #http://www.python.org
 
url = input('Please enter the URL: ')
domain = url[:-4]
print("Domain name is: " + domain)
# Please enter the URL: www.naver.com
# Domain name is: www.naver

[start:end:step]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(numbers[2:5]) # [3, 4, 5]
print(numbers[:]) # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
 
# copy
numbers2 = numbers[:]
print(numbers2) # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
 
#[start:end:step]
print(numbers[0:10:1]) # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(numbers[0:10:2]) # [1, 3, 5, 7, 9]
print(numbers[::2]) # [1, 3, 5, 6, 7]
print(numbers[3:6]) # [4, 5, 6]
print(numbers[3:6:3]) # [4]
print(numbers[::3]) # [1, 4, 7, 10]
 
#-가 붙으면 거꾸
print(numbers[10:0:-2]) # [10, 8, 6, 4, 2]
print(numbers[:5:-1]) # [10, 9, 8, 7]
print(numbers[:5:-2]) # [10. 8]

3. Adding / multiplying

 #Add
print([1, 3, 4] + [2,1]) # [1, 3, 4, 2, 1]
 
# multiply
sequence = [None] * 10
print(sequence) # [None, None, None, None, None, None, None, None, None, None]
 
#print a sentence in a center "box" of correct width
sentence = input("Sentence: ")
screen_width = 80
text_width = len(sentence)
box_width = text_width + 6
left_margin = (screen_width-box_width) // 2
 
print()
print(' '*left_margin+'+' + '-'*(box_width-2)+'+')
print(' '*left_margin+'|  ' + ' '*text_width +'  |')
print(' '*left_margin+'|  ' + sentence +'  |')
print(' '*left_margin+'|  ' + ' '*text_width+'  |')
print(' '*left_margin+'+' + '-'*(box_width-2)+'+')
 
#                                   +--------+
#                                   |        |
#                                   |  okay  |
#                                   |        |
#                                   +--------+

4. membership

권한이나 특정 문자 등을 찾을때, 유용하다

permission = 'rw'
print('w' in permission) # True
print('x' in permission) # False
 
# find a spam mail
subject = '$$$ Get rich now!! $$$'
print('$$$' in subject) # True

members = [
    ['albert', '1234'],
    ['jiyoung', '4242'],
    ['smith', '7524'], 
    ['babo', '4321']
]
 
username = input('User name: ')
pin = input('PIN code: ')
 
if [username, pin] in members:
    print('Access granted')
    # User name: jiyoung
    # PIN code: 4242
    # Access granted
else: 
    print('Check your User name or PIN number')
    # User name: babo
    # PIN code: 1234
    # Check your User name or PIN number

5. 기타

numbers = [1, 100, 1000, 10000]
print(len(numbers)) # 4
print(max(numbers)) # 10000
print(min(numbers)) # 1

범위 밖으로는 추가 할수가 없다.

x=[1, 1, 1]
print(x[1]) # 1
 
# in-place modification (mutable!)
x[1] = 2 # 1 -> 2로 바꿈 
print(x) # [1, 2, 1]
 
# len(x) = 3이기 떄문 
x[10] = 5 #IndexError: list assignment index out of range

6. List 함수

# list()
print(list('Hello')) # ['H', 'e', 'l', 'l', 'o']
 
a = list('HELLO')
print(a) # ['H', 'E', 'L', 'L', 'O']
 
# .join
print(''.join(a)) # HELLO
print('!'.join(a)) # H!E!L!L!O

2) del

names = ['Alice', 'Beth', 'Cecil', 'Deisy']
del names[1]
print(names) #['Alice', 'Cecil', 'Deisy']

3) assign't

name = list('Perl')
print(name) # ['P', 'e', 'r', 'l']
 
name[2:] = list('ar') # [a, r]
print(name) # ['P', 'e', 'a', 'r']

4) 함수를 이용하지 않아도 list 그 자체로도 사용이 가능하긴 하다

numbers = [1, 5]
numbers[1:1] = [2, 3, 4, 6]
print(numbers) # [1, 2, 3, 4, 6, 5]
 
# del()
numbers[1:3] = []
print(numbers) # [1, 4, 6, 5]

5) append()

# append()
lst = [1, 2, 3]
lst.append(5)
print(lst) # [1, 2, 3, 5]

8) index()

# index()
heroes  = ['we', 'are', 'the', 'heroes', 'who', 'say', 'of', 'course']
print(heroes.index('who')) #4
print(heroes.index('heroes')) #3
print(heroes.index('what')) #ValueError: 'what' is not in list

9) insert()

# insert()
numbers = [1, 2, 3, 4, 5, 7]
numbers.insert(3, 'five')
print(numbers) # [1, 2, 3, 'five', 4, 5, 7]
 
 
numbers = [1, 2, 3, 4, 5, 7]
numbers[3:3] = ['five']
print(numbers) # [1, 2, 3, 'five', 4, 5, 7]

10) pop(), remove()

# pop()
x = [1, 2, 3]
print(x.pop()) #3
print(x) # [1, 2]
print(x.pop()) #2
print(x) # [1]
print(x.pop()) #1
print(x) # []
 
#remove()
heroes = ['we', 'are', 'the', 'heroes', '!']
heroes.remove('!')
print(heroes) # ['we', 'are', 'the', 'heroes']

# reverse()
heroes = ['we', 'are', 'the', 'heroes', '!']
heroes.reverse()
print(heroes) # ['!', 'heroes', 'the', 'are', 'we']
 
heroes.reverse()
print(heroes) # ['we', 'are', 'the', 'heroes', '!']

# reversed()
print(list(reversed(heroes))) # ['!', 'heroes', 'the', 'are', 'we']

12) sort()

# sort()
x = [1, 3, 4, 5, 12, 15]
y = x.sort()
print(y) # None
 
x.sort()
print(x) # [1, 3, 4, 5, 12, 15]

*주의*

sort()된 값을 바로 저장할 수 없다. 

값을 저장하려면 2가지 방법을 이용할 수 있다.

# 저장 ver.1
x = [1, 3, 4, 5, 12, 15]
y = x
y.sort()
print(y) # [1, 3, 4, 5, 12, 15]
 
# 저장 ver.2
y = sorted(x)
print(y) # [1, 3, 4, 5, 12, 15]

*고급 sorting : https://wiki.python.org/HowTo/Sorting