Meaning
Creates a memoryview of a bytes-like object, slices it to obtain a sub‑range, and converts the view back to a new bytes object. This provides a zero‑copy view for slicing before materializing the slice as an independent bytes object. Use it when you need to extract a slice from a large bytes buffer without incurring copy overhead until the final conversion.
Primary Function
Binary data slicing and conversion
Communicative Purpose
Obtain a contiguous slice of binary data as an independent bytes object without copying the original data until conversion.
Pattern
memoryview(bytes_obj)[start:stop].tobytes()
Core Structure
memoryview(...)[...:...].tobytes()
Função primária
Binary data slicing and conversion
Propósito comunicativo
Obtain a contiguous slice of binary data as an independent bytes object without copying the original data until conversion.
Situações de gatilho
Networking: extracting a sub‑range from a received byte buffer; File parsing: reading a segment of a large binary file without copying; C extension interop: passing a slice of bytes to a C function expecting a pointer
Contextos
Low‑level I/O, networking, file format parsing, performance‑critical code that handles binary data.
Padrão
memoryview(bytes_obj)[start:stop].tobytes()
Estrutura central
memoryview(...)[...:...].tobytes()
Slots de substituição
bytes_obj: bytes-like object, start: int, stop: int
Colocados típicos
- struct.unpack
- bytes.fromhex
- io.BytesIO
Substituições comuns
- bytes_obj[start:stop] (direct slicing) when copying is acceptable
- memoryview(obj).cast('B')[start:stop].tobytes() for different formats.
Erros comuns
Assuming the slice returns a memoryview that can be used directly as bytes; forgetting .tobytes() yields a memoryview, not bytes; using negative indices incorrectly; attempting to mutate the original bytes via the view (which is read‑only for bytes).
Similar / contraste
bytearray slicing (mutable) vs memoryview slicing (read‑only for bytes); using struct.pack/unpack for binary data interpretation.
Interferências
Coming from C: expecting pointer arithmetic; memoryview does not allow mutation of the underlying bytes object.
Família do chunk
- memoryview slicing
- bytes slicing
- bytearray slicing
- struct module unpacking
Nuance
The memoryview shares memory with the original bytes until .tobytes() is called, after which a new independent bytes object is created; the slice is read‑only; for mutable bytearray, the view is writable.
Efeito pragmático
Provides a zero‑copy view for slicing, reducing memory overhead before materializing the slice as bytes.
Dica de memória
Think of a window (memoryview) over a byte stream that you can slide and then snapshot.
Nota
The resulting bytes object is independent; modifications to it do not affect the original bytes.
Upgrade path
Using memoryview.cast to change format, or using numpy.ndarray for more complex manipulations.
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