https://github.com/cuspaceflight/magicmemoryview

Magic memoryview() style casting for Cython
https://github.com/cuspaceflight/magicmemoryview

Last synced: about 2 months ago
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Magic memoryview() style casting for Cython

• Host: GitHub
• URL: https://github.com/cuspaceflight/magicmemoryview
• Owner: cuspaceflight
• Created: 2014-08-03T11:29:18.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2014-08-10T12:19:42.000Z (over 10 years ago)
• Last Synced: 2024-08-06T05:36:32.771Z (5 months ago)
• Language: Python
• Size: 175 KB
• Stars: 3
• Watchers: 4
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.rst

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README

        
A helper / hack to allow us to cast a ``mmap.mmap`` or other buffer to

a Cython pointer of the correct type.

Cython is capable of casting a lot of things to a C pointer of the

correct type, especially with the aid of ``memoryview``. However,

in Python 2, ``memoryview`` lacks the ``memoryview.cast`` method

(so Cython won't let us change the dimensions of the array). Further,

both Python 2 and 3 require the memory map to be writable (making

the pointer type ``const`` does not seem to help here either).

This class takes a (possibly read-only) memmap object, and produces a

Python object with a ``__getbuffer__`` method that returns The Right Thing.

*It pretends that the underlying buffer is writable* to make Cython

happy. If you give it a read-only buffer, and try to write to the result,

then you will have a bad time.

When a Python object is cast by Cython to a pointer, it holds a

reference to the underlying Python object in order to prevent the

memory to which it refers being garbage collected. The ``MagicMemoryView``

in turn keeps a reference to the underlying data, so everything should

behave as expected.

Usage::

    from magicmemoryview import MagicMemoryView

    cdef double data[:, :, :]

    data = MagicMemoryView(source_buffer, (24, 12, 25), "d")