# 每轮只取得一行；行尾换行仍保留，空白行也不是文件结束。
from pathlib import Path

path = Path("lines.txt")
path.write_text("Python\n\nNumPy\n", encoding="utf-8")
with path.open(encoding="utf-8") as stream:
    for number, line in enumerate(stream, start=1):
        print(number, repr(line))
    print("末尾", repr(stream.readline()))

# 一次取最多四个字节，不必先把完整文件读进内存。
from pathlib import Path

path = Path("chunks.bin")
path.write_bytes(b"abcdefghi")
total = 0
with path.open("rb") as stream:
    while True:
        chunk = stream.read(4)
        if not chunk:
            break
        total += len(chunk)
        print(chunk)
print("总字节数", total)

# batched 消耗文件迭代器，每次交出最多两行；转换后立即处理这批数据。
from itertools import batched
from pathlib import Path

path = Path("batches.txt")
path.write_text("20\n35\n45\n", encoding="utf-8")
with path.open(encoding="utf-8") as stream:
    for lines in batched(stream, 2):
        values = [int(line) for line in lines]
        print(values, sum(values))