[프로그래머스] 파이썬을 파이썬답게 정리

https://school.programmers.co.kr/learn/courses/4008

파이썬을 파이썬답게

몫과 나머지

a = 45
b = 6

# 일반사람 코드
print (a // b, a%b)

# divmod를 사용한 코드
print(*divmod(a, b))

• divmod이 안좋음. 작은 숫자를 다룰때 a//b, a%b보다 느림

n진법을 10진법으로 바꾸기

num = '3212'
base = 4

# int는 함수의 진법변환 지원
answer = int(num, base)

문자열 정렬

s = "test str"
n = 10

print(s.ljust(n)) # 좌측 정렬
print(s.center(n)) # 가운데 정렬
print(s.rjust(n))# 우측 정렬

소문자, 대문자, 숫자, 대소문자 다 가져오기

import string 

string.ascii_lowercase # 소문자 abcdefghijklmnopqrstuvwxyz
string.ascii_uppercase # 대문자 ABCDEFGHIJKLMNOPQRSTUVWXYZ
string.ascii_letters # 대소문자 모두 abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
string.digits # 숫자 0123456789

원본을 유지한채 리스트 구하기(sorted) : zip

• zip 함수 이용하기
  • zip : Returns an iterator of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables.
  • ex)use multiple Iterables at the same time

    mylist = [1, 2, 3]
    new_list = [40, 50, 60]
    for i in zip(mylist, new_list):
    print (i)
    
    # (1, 40)
    # (2, 50)
    # (3, 60)
    - ex) turn over the list

 

mylist = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
new_list = list(map(list, zip(*mylist)))

# output
# new_list = [[1, 4, 7], [2, 5, 8], [3, 6, 9]]

• ex) create dictionary use key list and value list

  animals = ['cat', 'dog', 'lion']
  sounds = ['meow', 'woof', 'roar']
  answer = dict(zip(animals, sounds)) # {'cat': 'meow', 'dog': 'woof', 'lion': 'roar'}

• ex) difference bewteen list i and i+1

  answer = []
  for number1, number2 in zip(list, list[1:]):
     answer.append(abs(number1 - number2))

Convert type(str -> int) : map

list1 = ['1', '2', '3']
list2 = list(map(int, list1))

return list length using map fucntion

• map : create new list (not change original list)

  input_list = [[1,2,3], [1,2,3,4,5,6]]
  #output -> [3, 6]
  
  answer = list(map(len, input_list)
  
  ## _attache the all list member : join_

 

list = ['a', 'b', 'c']

result = "".join(list)
#output -> 'abc'

Cartesian product : itertools

import itertools as it 

iterable1 = 'ABCD'
iterable2 = 'xy'
iterable3 = '1234'
print(list(it.product(iterable1, iterable2, iterable2)))

make the list to flatten

my_list = [[1, 2], [3, 4], [5, 6]]

# 방법 1 - sum 함수
answer = sum(my_list, [])

# 방법 2 - itertools.chain
import itertools
list(itertools.chain.from_iterable(my_list))

# 방법 3 - itertools와 unpacking
import itertools
list(itertools.chain(*my_list))

# 방법 4 - list comprehension 이용
[element for array in my_list for element in array]

# 방법 5 - reduce 함수 이용 1
from functools import reduce
list(reduce(lambda x, y: x+y, my_list))

# 방법 6 - reduce 함수 이용 2
from functools import reduce
import operator
list(reduce(operator.add, my_list))

• chain :It is a function that takes a series of iterables and returns one iterable. It groups all the iterables together and produces a single iterable as output. Its output cannot be used directly and thus explicitly converted into iterables. This function come under the category iterators terminating iterators.

  def chain(*iterables):
     for it in iterables:
       for each in it:
           yield each

• functools.reduce : Built-in mutable sequence. If no argument is given, the constructor creates a new empty list. The argument must be an iterable if specified.

순열과 조합 - combinations, permutations

import itertools

pool = ['A', 'B', 'C']
print(list(map(''.join, itertools.permutations(pool)))) # 3개의 원소로 수열 만들기
print(list(map(''.join, itertools.permutations(pool, 2)))) # 2개의 원소로 수열 만들기

automatic string casting in class

class Coord(object):
    def __init__ (self, x, y):
        self.x, self.y = x, y
    def __str__ (self):
        return '({}, {})'.format(self.x, self.y)

point = Coord(1, 2)

init maximum value

min_val = float('inf')

simply file read

with open('myfile.txt') as file:
    for line in file.readlines():
        print(line.strip().split('\t'))