Python 3.7+Async programmingterm

asyncio.BufferedProtocol

protocols and transports

A streaming protocol with a manual buffer: the loop asks for a buffer via get_buffer(), writes data into it and reports the length in buffer_updated(). Added in Python 3.7.

Syntax

class P(asyncio.BufferedProtocol): def get_buffer(self, sizehint): ...; def buffer_updated(self, nbytes): ...

Learners rarely need this layer: streams (asyncio.open_connection() and asyncio.start_server()) cover TCP, and asyncio.create_subprocess_exec() covers processes. BufferedProtocol is an optimisation over Protocol: data lands straight in your bytearray instead of a fresh bytes object per chunk. It only pays off for very large streams; get_buffer() must return a non-empty writable buffer, and you must read exactly nbytes from buffer_updated(), not the whole buffer — the tail holds leftovers from earlier chunks.

Examples

import asyncio
import socket
class Reader(asyncio.BufferedProtocol):
    def __init__(self):
        self.buf = bytearray(16)
        self.chunks = []
    def get_buffer(self, sizehint):
        return self.buf
    def buffer_updated(self, nbytes):
        self.chunks.append(bytes(self.buf[:nbytes]))  # ровно nbytes, не весь буфер
async def main():
    loop = asyncio.get_running_loop()
    left, right = socket.socketpair()
    transport, proto = await loop.create_connection(Reader, sock=left)
    right.sendall(b'hello')
    await asyncio.sleep(0.01)
    print(proto.chunks)  # → [b'hello']
    transport.close()
    right.close()
asyncio.run(main())

asyncio.BufferedProtocol

Syntax

Examples

See also