[Python] Generator

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def gen():
    x = [1,2,3]
    for i in x:
        yield i

g = gen()

print(type(g))
# <class 'generator'>

print(g.__dir__())
# ['__repr__', '__getattribute__', '__iter__', '__next__', '__del__', 'send', 'throw', 'close', 'gi_frame', 'gi_running', 'gi_code', '__name__', '__qualname__', 'gi_yieldfrom', '__doc__', '__hash__', '__str__', '__setattr__', '__delattr__', '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__', '__init__', '__new__', '__reduce_ex__', '__reduce__', '__subclasshook__', '__init_subclass__', '__format__', '__sizeof__', '__dir__', '__class__']
# __iter__, __next__ 함수 존재

print(next(g))
# 1
print(next(g))
# 2

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# 이런식으로 쉽게 Iterator를 만들 수 있다
def number_generator(stop):
    n = 0              
    while n < stop:    
        yield n        
        n += 1

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# 위에서 만든 것과 동일한 결과
def number_generator():
    x = [1, 2, 3]
    yield from x

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def number_generator(stop):
    n = 0
    while n < stop:
        yield n
        n += 1
 
def three_generator():
    yield from number_generator(3)
 
for i in three_generator():
    print(i)

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# 리스트
[i for i in range(50) if i % 2 == 0]
# generator
(i for i in range(50) if i % 2 == 0)

# 메모리 절약
import sys
list_size = sys.getsizeof( [i for i in range(50) if i % 2 == 0])
get_size = sys.getsizeof((i for i in range(50) if i % 2 == 0))

print(list_size) # 312
print(get_size)  # 112