"""
Урок 56. Генераторы — весь код примеров одним файлом.

Источник: subjects/python-fundamentals/course/lessons/56-generators/examples.html
Файл собран автоматически (tools/build_lesson_examples.py): правьте страницу урока.
Запуск: python lesson-56.py
"""



# ====================================================================
# Пример 1. Вызов не выполняет тело функции
# ====================================================================
def simple_generator():
    print("Старт")
    yield 1
    print("Середина")
    yield 2
    print("Финиш")


gen = simple_generator()
print(gen)                  # <generator object simple_generator at 0x...>
print(type(gen))             # <class 'generator'>

print(next(gen))
# Старт
# 1
print(next(gen))
# Середина
# 2
try:
    print(next(gen))
except StopIteration:
    print("StopIteration")
# Финиш
# StopIteration


# ====================================================================
# Пример 2. next() со значением по умолчанию
# ====================================================================
def limited():
    yield "a"
    yield "b"


g = limited()
print(next(g))                      # a
print(next(g))                      # b
print(next(g, "конец данных"))      # конец данных
print(next(g, "конец данных"))      # конец данных — можно звать сколько угодно раз


# ====================================================================
# Пример 3. Генератор одноразовый
# ====================================================================
def my_range(start, end):
    current = start
    while current < end:
        yield current
        current += 1


generator = my_range(1, 4)
print(list(generator))   # [1, 2, 3]
print(list(generator))   # [] — уже исчерпан

print(list(my_range(1, 4)))   # [1, 2, 3] — новый вызов = новый генератор


# ====================================================================
# Пример 4. Зачем вообще ленивость: генератор против списка по памяти
# ====================================================================
import sys

list_comp = [x * x for x in range(1000)]
gen_expr = (x * x for x in range(1000))

print(sys.getsizeof(list_comp))   # 8856
print(sys.getsizeof(gen_expr))    # 208

print(sum(list_comp))   # 332833500
print(sum(gen_expr))    # 332833500 — тот же результат


# ====================================================================
# Пример 5. Бесконечный генератор и управляемая остановка
# ====================================================================
from itertools import islice


def infinite_counter(start=1):
    while True:
        yield start
        start += 1


counter = infinite_counter()
print(list(islice(counter, 5)))   # [1, 2, 3, 4, 5]
print(next(counter))              # 6 — счётчик не сбросился, продолжает с того же места


# ====================================================================
# Пример 6. close() завершает генератор досрочно
# ====================================================================
def sensor_reader(values):
    for value in values:
        yield value


sensor = sensor_reader([10, 20, 30, 40, 50])
collected = []
for value in sensor:
    collected.append(value)
    if value >= 30:
        sensor.close()
        break

print(collected)   # [10, 20, 30]

try:
    next(sensor)
except StopIteration:
    print("StopIteration after close")   # StopIteration after close


# ====================================================================
# Пример 7. yield from: делегирование и рекурсивный «расплющиватель»
# ====================================================================
def flatten(nested):
    for item in nested:
        if isinstance(item, list):
            yield from flatten(item)
        else:
            yield item


print(list(flatten([1, [2, [3, 4]], 5])))   # [1, 2, 3, 4, 5]


def letters():
    yield from "AB"     # yield from работает с любым iterable, не только с генератором
    yield from [1, 2]


print(list(letters()))   # ['A', 'B', 1, 2]


# ====================================================================
# Пример 8. send(): значения можно передавать внутрь генератора
# ====================================================================
def running_total():
    total = 0
    while True:
        value = yield total
        total += value


acc = running_total()
print(next(acc))       # 0  — запускаем генератор до первого yield
print(acc.send(10))    # 10
print(acc.send(5))     # 15
print(acc.send(-3))    # 12


# ====================================================================
# Пример 9. Генератор против класса-итератора: тот же результат, меньше кода
# ====================================================================
class RangeIterator:
    def __init__(self, start, end):
        self.current = start
        self.end = end

    def __iter__(self):
        return self

    def __next__(self):
        if self.current >= self.end:
            raise StopIteration
        value = self.current
        self.current += 1
        return value


print(list(RangeIterator(1, 4)))   # [1, 2, 3]
print(list(my_range(1, 4)))        # [1, 2, 3] — тот же результат, 6 строк вместо 11


# ====================================================================
# Пример 10. Конвейер из нескольких генераторов
# ====================================================================
def read_lines(text):
    for line in text.splitlines():
        yield line


def non_empty(lines):
    for line in lines:
        stripped = line.strip()
        if stripped:
            yield stripped


def numbered(lines):
    for index, line in enumerate(lines, start=1):
        yield f"{index}: {line}"


report = """Alice: 90

Bob: 75

Carol: 88"""

pipeline = numbered(non_empty(read_lines(report)))
for row in pipeline:
    print(row)
# 1: Alice: 90
# 2: Bob: 75
# 3: Carol: 88


# ====================================================================
# Пример 11. Ловушка: один и тот же генератор нельзя скормить двум потребителям
# ====================================================================
def make_range():
    return my_range(1, 4)


shared = my_range(1, 4)
first_pass = list(shared)
second_pass = list(shared)
print(first_pass, second_pass)   # [1, 2, 3] []

fresh_first = list(make_range())
fresh_second = list(make_range())
print(fresh_first, fresh_second)   # [1, 2, 3] [1, 2, 3]