Python 3.3+Linux · macOSosfunction

os.writev

os — positional I/O

Write to a descriptor from multiple buffers (gather write). Availability: Unix.

Syntax

os.writev(...)

It writes several bytes-like objects in one system call — no b''.join beforehand and no separate writes. That cuts kernel round-trips when sending a header and a body. It may write only part of the data, and the rest, possibly from the middle of one buffer, must then be written by you.

Examples

import os
fd = os.open('writev-demo.txt', os.O_RDWR | os.O_CREAT | os.O_TRUNC)  # временный файл для опытов
print(os.writev(fd, [b'name;', b'age\n']))  # → 9 — обе части записаны одним системным вызовом
print(os.writev(fd, [b'Ann;', b'20\n']))  # → 7 — writev пишет с текущей позиции, дописывая в конец
print(os.pread(fd, 16, 0))  # → b'name;age\nAnn;20\n'
print(os.writev(fd, []))  # → 0 — пустой список буферов ничего не пишет

See also

Common errors

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