memoryview

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memoryview#

memoryview is a zero-copy view over a bytes-like object (bytes, bytearray, array.array, numpy array, anything supporting the buffer protocol). Slicing produces another view; no copy.

buf = bytearray(65536)
mv  = memoryview(buf)
sock.recv_into(mv[1024:2048])    # write directly into buf
header  = mv[:24]                 # no copy
payload = mv[24:]                 # no copy

Conversion to bytes happens only when the operator asks for it (bytes(mv[:24])) or when a function copies the slice internally.

memoryview exposes cast for reinterpreting the buffer as a different fixed-width type, useful for treating a byte buffer as an array of integers.

mv = memoryview(bytearray(16))
mv32 = mv.cast("I")              # view as unsigned 32-bit ints
mv32[0] = 0xdeadbeef

Always release a memoryview over a bytearray before trying to resize the buffer; the view holds a reference that freezes the size.

buf = bytearray(b"abcdef")
mv = memoryview(buf)
try:
    ... # use mv
finally:
    mv.release()
buf.extend(b"more")              # safe now

References#

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