Python has mutable and immutable objects:
Mutables:
- bytearray
- list
- …
Immutables:
- string
- bytes
- …
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buf = bytearray(b"hello world")
mv = memoryview(buf)
mv2 = mv[6:11] # refers to the same bytes as buf[6:11]
mv2.tobytes() # => b"world", but buf isn’t duplicated in memory until you call tobytes()
- Bytes is immutable, meaning once created, its contents cannot be changed. So any slice of it will be a new object
- By default, slice of a mutable object is also a new object
Memory View
It returns the memory of the underlying object. To avoid copies, use memoryview:
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buf = bytearray(1024)
view = memoryview(buf)[100:] # no copy
n = sock.recv_into(view) # writes *directly* into buf[100:100+n]
- The
memoryviewobject of a mutable object is writable, otherwise it’d be read-only for an immutable
Advanced buffer‐protocol features
You can cast a memoryview object to other element types, like raw bytes as 32-bit ints
