"""
Урок 55. Summary session 14 — весь код примеров одним файлом.

Источник: subjects/python-fundamentals/course/lessons/55-summary-session-14/examples.html
Файл собран автоматически (tools/build_lesson_examples.py): правьте страницу урока.
Запуск: python lesson-55.py
"""



# ====================================================================
# Пример 1. Режимы open() и безопасное закрытие через with
# ====================================================================
with open("report.txt", "w", encoding="utf-8") as file:
    file.write("первая строка\n")
print("Файл создан режимом 'w'")

with open("report.txt", "a", encoding="utf-8") as file:
    file.write("вторая строка\n")
print("Дописали режимом 'a'")

try:
    with open("report.txt", "x", encoding="utf-8") as file:
        pass
except FileExistsError as error:
    print("FileExistsError:", error)
    # [Errno 17] File exists: 'report.txt'

with open("report.txt", "r", encoding="utf-8") as file:
    print(repr(file.read()))
    # 'первая строка\nвторая строка\n'


# ====================================================================
# Пример 2. read(), readline(), readlines() — три разные формы результата
# ====================================================================
with open("report.txt", "r", encoding="utf-8") as file:
    print("read():", repr(file.read()))
    # read(): 'первая строка\nвторая строка\n'  — вся строка целиком

with open("report.txt", "r", encoding="utf-8") as file:
    print("readline():", repr(file.readline()))          # 'первая строка\n'
    print("readline() ещё раз:", repr(file.readline()))  # 'вторая строка\n'

with open("report.txt", "r", encoding="utf-8") as file:
    print("readlines():", file.readlines())
    # ['первая строка\n', 'вторая строка\n']  — список строк


# ====================================================================
# Пример 3. Запись: write() и writelines()
# ====================================================================
lines = ["строка A\n", "строка B\n", "строка C\n"]
with open("batch.txt", "w", encoding="utf-8") as file:
    file.writelines(lines)

with open("batch.txt", "r", encoding="utf-8") as file:
    for line in file:
        print(line.strip())
# строка A
# строка B
# строка C


# ====================================================================
# Пример 4. iter(), next() и StopIteration
# ====================================================================
values = iter([10, 20, 30])
print(next(values))            # 10
print(next(values))            # 20
print(next(values, "конец"))   # 30
print(next(values, "конец"))   # конец — элементы закончились, но исключения нет

values2 = iter([1, 2])
try:
    next(values2)
    next(values2)
    next(values2)   # элементов больше нет
except StopIteration:
    print("StopIteration поймали вручную")


# ====================================================================
# Пример 5. Итератор одноразовый — список нет
# ====================================================================
it = iter([1, 2, 3])
print(list(it))   # [1, 2, 3]
print(list(it))   # []  — уже нечего отдавать

numbers_list = [1, 2, 3]
print(list(numbers_list))   # [1, 2, 3]
print(list(numbers_list))   # [1, 2, 3] — список можно обходить сколько угодно раз


# ====================================================================
# Пример 6. Генераторное выражение: ленивость, память, без индексации
# ====================================================================
numbers = [1, 2, 3, 4, 5]
squares_gen = (x ** 2 for x in numbers)
squares_list = [x ** 2 for x in numbers]

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

try:
    squares_gen[0]           # индексация недоступна
except TypeError as error:
    print("TypeError:", error)
    # 'generator' object is not subscriptable

print(list(squares_gen))   # [1, 4, 9, 16, 25] — значения вычисляются здесь


# ====================================================================
# Пример 6. Генераторное выражение: ленивость, память, без индексации
# ====================================================================
import sys

big_gen = (x ** 2 for x in range(1, 1_000_001))
big_list = [x ** 2 for x in range(1, 1_000_001)]

print(sys.getsizeof(big_gen), "байт — генератор")   # 208 байт — генератор
print(sys.getsizeof(big_list), "байт — список")     # 8448728 байт — список


# ====================================================================
# Пример 7. any(), all(), sum() с генераторным выражением
# ====================================================================
nums = [3, 7, 12, 5, 9]
print(any(n > 10 for n in nums))            # True
print(all(n > 0 for n in nums))              # True
print(sum(n for n in nums if n % 2 == 0))    # 12 — сумма только чётных

def probe(n):
    print("  проверяю", n)
    return n > 10

print(any(probe(n) for n in nums))
#   проверяю 3
#   проверяю 7
#   проверяю 12
# True   — до 5 и 9 проверка не дошла, результат уже известен


# ====================================================================
# Пример 8. itertools.chain: пройти несколько последовательностей как одну
# ====================================================================
import itertools

fruits = ["apple", "banana"]
vegetables = ["carrot", "tomato"]

for item in itertools.chain(fruits, vegetables):
    print(item)
# apple
# banana
# carrot
# tomato


# ====================================================================
# Пример 9. itertools.count: бесконечный счётчик и как его безопасно ограничить
# ====================================================================
counter = itertools.count(start=10, step=5)
first_three = list(itertools.islice(counter, 3))
print(first_three)   # [10, 15, 20]


# ====================================================================
# Пример 10. itertools.product и itertools.permutations: комбинаторика без вложенных циклов
# ====================================================================
sizes = ["S", "M"]
colors = ["red", "blue"]
print(list(itertools.product(sizes, colors)))
# [('S', 'red'), ('S', 'blue'), ('M', 'red'), ('M', 'blue')]

print(list(itertools.permutations([1, 2, 3], 2)))
# [(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]


# ====================================================================
# Пример 11. Собираем всё: файл + генераторное выражение (задание 3 урока)
# ====================================================================
with open("numbers.txt", "w", encoding="utf-8") as file:
    for n in range(1, 11):
        file.write(str(n) + "\n")

with open("numbers.txt", "r", encoding="utf-8") as file:
    total = sum(int(line.strip()) ** 2 for line in file if line.strip())

print("Сумма квадратов:", total)   # 385