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Diffstat (limited to 'docs/src/userguide/memoryviews.rst')
| -rw-r--r-- | docs/src/userguide/memoryviews.rst | 33 |
1 files changed, 25 insertions, 8 deletions
diff --git a/docs/src/userguide/memoryviews.rst b/docs/src/userguide/memoryviews.rst index 328831e86..285cc67ea 100644 --- a/docs/src/userguide/memoryviews.rst +++ b/docs/src/userguide/memoryviews.rst @@ -20,6 +20,9 @@ A memoryview can be used in any context (function parameters, module-level, cdef class attribute, etc) and can be obtained from nearly any object that exposes writable buffer through the `PEP 3118`_ buffer interface. +.. _`PEP 3118`: https://www.python.org/dev/peps/pep-3118/ + + .. _view_quickstart: Quickstart @@ -39,6 +42,7 @@ This code should give the following output:: Memoryview sum of Cython array is 1351 Memoryview sum of C memoryview is 451 +.. _using_memoryviews: Using memoryviews ================= @@ -56,16 +60,11 @@ A complete 3D view:: cdef int[:,:,:] view3D = exporting_object -A 2D view that restricts the first dimension of a buffer to 100 rows -starting at the second (index 1) and then skips every second (odd) row:: - - cdef int[1:102:2,:] partial_view = exporting_object - -This also works conveniently as function arguments: +They also work conveniently as function arguments: .. code-block:: cython - def process_3d_buffer(int[1:102:2,:] view not None): + def process_3d_buffer(int[:,:,:] view not None): ... The ``not None`` declaration for the argument automatically rejects @@ -80,6 +79,12 @@ three dimensional buffer into a function that requires a two dimensional buffer will raise a ``ValueError``. +To use a memory view on a numpy array with a custom dtype, you'll need to +declare an equivalent packed struct that mimics the dtype: + +.. literalinclude:: ../../examples/userguide/memoryviews/custom_dtype.pyx + + Indexing -------- @@ -234,6 +239,8 @@ NumPy arrays support this interface, as do :ref:`view_cython_arrays`. The data array to themselves be pointers; Cython memoryviews do not yet support this. +.. _`new style buffers`: https://docs.python.org/3/c-api/buffer.html + .. _view_memory_layout: Memory layout @@ -660,6 +667,16 @@ object handling. For the details of how to compile and call functions in C files, see :ref:`using_c_libraries`. -.. _GIL: http://docs.python.org/dev/glossary.html#term-global-interpreter-lock +Performance: Disabling initialization checks +============================================ + +Every time the memoryview is accessed, Cython adds a check to make sure that it has been initialized. + +If you are looking for performance, you can disable them by setting the +``initializedcheck`` directive to ``False``. +See: :ref:`compiler-directives` for more information about this directive. + + +.. _GIL: https://docs.python.org/dev/glossary.html#term-global-interpreter-lock .. _NumPy: https://docs.scipy.org/doc/numpy/reference/arrays.ndarray.html#memory-layout .. _example: https://docs.scipy.org/doc/numpy/reference/arrays.indexing.html |