generator คืออะไร และสร้างอย่างไร?

ฝึกทำโจทย์สัมภาษณ์งานเขียนโค้ดด้วย Python

Kirill Smirnov

Data Science Consultant, Altran

นิยาม

Generator - อ็อบเจกต์ iterable พิเศษที่สร้างจากฟังก์ชันที่มีคีย์เวิร์ด yield อยู่ในเนื้อหา

def func():
    # Return a value from super complex calculations
    return 0

result = func()
print(result)

def func():
    # Yield a value from super complex calculations
    yield 0

result = func()
print(result)

<generator object result at 0x105736e10>

def func():
    # Yield a value from super complex calculations
    yield 0

result = func()

for item in result:
    print(item)

def func():
    yield 0
    yield 1
    yield 2

result = func()
for item in result:
    print(item)

0
1
2

def func(n):
    for i in range(0, n):
        yield 2*i

result = func(3)
for item in result:
    print(item)

0
2
4

def func(n):
    for i in range(0, n):
        yield 2*i

result = func(5)

list(result)

[0, 2, 4, 6, 8]

Generator เป็นทั้ง Iterable และ Iterator

def func(n):
    for i in range(0, n):
        yield 2*i

result = func(3)

next(result)

next(result)

next(result)

next(result)

StopIteration

def func(n):
    for i in range(0, n):
        yield 2*i

result = func(3)

for item in result:
    print(item)

0
2
4

for item in result:
    print(item)

# nothing

result = func(3)
for item in result:
    print(item)

0
2
4

def func(n):
    for i in range(0, n):
        yield 2*i

result = func(3)
list(result)

[0, 2, 4]

list(result)

[]

result = func(3)
list(result)

[0, 2, 4]

result = [2*i for i in range(0, 3)]
print(result)

[0, 2, 4]

result = (2*i for i in range(0, 3))
print(result)

<generator object result at 0x105736e10>

result = (2*i for i in range(0, 3))

for item in result:
    print(item)

0
2
4

next(result)

StopIteration

[1, 3, 2, 4, 3, 5]

def create_jump_sequence(n):
    for i in range(1, n-1):
        yield i
        yield i+2

jump_sequence = create_jump_sequence(5)
list(jump_sequence)

[1, 3, 2, 4, 3, 5]

[1, 3, 2, 4, 3, 5, 4, 6, 5, 7, ...]

def create_jump_sequence(n):
    for i in range(1, n-1):
        yield i
        yield i+2

jump_sequence = create_jump_sequence(500)
next(jump_sequence)

def create_inf_generator():
    while True:
        yield 'I am infinite!'

inf_generator = create_inf_generator()

next(inf_generator)

I am infinite

ฝึกทำโจทย์สัมภาษณ์งานเขียนโค้ดด้วย Python