memoryview

Properties

>>> dir(memoryview)
['__class__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__enter__', '__eq__', '__exit__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'c_contiguous', 'cast', 'contiguous', 'f_contiguous', 'format', 'hex', 'itemsize', 'nbytes', 'ndim', 'obj', 'readonly', 'release', 'shape', 'strides', 'suboffsets', 'tobytes', 'tolist', 'toreadonly']

Definition

A memoryview provides a zero-copy, sliceable view over binary data that supports the buffer protocol (e.g., bytes, bytearray, array, mmap). It allows reading and writing (if underlying object is writable) without copying the data.

>>> data = bytearray(b"hello")
>>> view = memoryview(data)
>>> view[0]
104
>>> view[0] = 72   # modify in place
>>> data
bytearray(b'Hello')

Creating memoryviews

>>> mv = memoryview(b"abc")              # from bytes (read-only)
>>> mv2 = memoryview(bytearray(b"abc"))  # from bytearray (read/write)

Slicing and casting

Memoryviews can be sliced without copying and cast to change the element format.

>>> mv = memoryview(bytearray(b"abcdef"))
>>> mv[2:4].tobytes()
b'cd'

# cast to view 16-bit unsigned integers (requires aligned size)
>>> mem = memoryview(bytearray(b"\x01\x00\x02\x00"))
>>> mem.cast("H").tolist()
[1, 2]

Attributes

• format — element format (PEP 3118 code)
• itemsize — size of each element in bytes
• nbytes — total bytes
• ndim, shape, strides — multi-dimensional info (for exporters that support it)
• readonly — True if underlying buffer is read-only
• obj — underlying object

Common methods

• tobytes() — return a bytes copy
• tolist() — return a list of elements
• cast(format, shape=None) — reinterpret view
• toreadonly() — get a read-only view
• release() — manually release the view (rarely needed; context manager supported)

Dunder methods

Dunder Method	Operation	Example (normal syntax)	Example (dunder call)
__getitem__	Index	view[0] → 104	view.__getitem__(0)
__setitem__	Modify data	view[0] = 72	view.__setitem__(0, 72)
__len__	Length	len(view) → 5	view.__len__()
__iter__	Iterate	for b in view	view.__iter__()
__eq__	Compare	view == memoryview(b'hello')	view.__eq__(other)
__enter__, __exit__	Context manager support	with memoryview(b'abc') as m:	m.__enter__() / m.__exit__()