File size: 1,119 Bytes
5eb110b | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | import contextlib
import inspect
class MyBuffer:
def __init__(self, data: bytes):
self.data = bytearray(data)
self.view = None
def __buffer__(self, flags: int) -> memoryview:
if flags != inspect.BufferFlags.FULL_RO:
raise TypeError("Only BufferFlags.FULL_RO supported")
if self.view is not None:
raise RuntimeError("Buffer already held")
self.view = memoryview(self.data)
return self.view
def __release_buffer__(self, view: memoryview) -> None:
assert self.view is view # guaranteed to be true
self.view.release()
self.view = None
def extend(self, b: bytes) -> None:
if self.view is not None:
raise RuntimeError("Cannot extend held buffer")
self.data.extend(b)
buffer = MyBuffer(b"capybara")
with memoryview(buffer) as view:
view[0] = ord("C")
with contextlib.suppress(RuntimeError):
buffer.extend(b"!") # raises RuntimeError
buffer.extend(b"!") # ok, buffer is no longer held
with memoryview(buffer) as view:
assert view.tobytes() == b"Capybara!"
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