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author | Ralf Gommers <ralf.gommers@gmail.com> | 2018-11-04 22:09:36 -0800 |
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committer | GitHub <noreply@github.com> | 2018-11-04 22:09:36 -0800 |
commit | bc8117727febce2168f21ff024286ced96b72020 (patch) | |
tree | 06e63b1b2c39f2f0873cadfbb5346cd8d0e02ab0 /doc/CAPI.rst.txt | |
parent | 619926d02588d44f184c310bceaff72eb62664a3 (diff) | |
parent | 1490fc84e8538c299bd029103ee824f913cb5d0a (diff) | |
download | numpy-bc8117727febce2168f21ff024286ced96b72020.tar.gz |
Merge pull request #12250 from mattip/add-docs-to-toc
DOC: add missing docs
Diffstat (limited to 'doc/CAPI.rst.txt')
-rw-r--r-- | doc/CAPI.rst.txt | 320 |
1 files changed, 0 insertions, 320 deletions
diff --git a/doc/CAPI.rst.txt b/doc/CAPI.rst.txt deleted file mode 100644 index ccee0fdb6..000000000 --- a/doc/CAPI.rst.txt +++ /dev/null @@ -1,320 +0,0 @@ -=============== -C-API for NumPy -=============== - -:Author: Travis Oliphant -:Discussions to: `numpy-discussion@python.org`__ -:Created: October 2005 - -__ https://scipy.org/scipylib/mailing-lists.html - -The C API of NumPy is (mostly) backward compatible with Numeric. - -There are a few non-standard Numeric usages (that were not really part -of the API) that will need to be changed: - -* If you used any of the function pointers in the ``PyArray_Descr`` - structure you will have to modify your usage of those. First, - the pointers are all under the member named ``f``. So ``descr->cast`` - is now ``descr->f->cast``. In addition, the - casting functions have eliminated the strides argument (use - ``PyArray_CastTo`` if you need strided casting). All functions have - one or two ``PyArrayObject *`` arguments at the end. This allows the - flexible arrays and mis-behaved arrays to be handled. - -* The ``descr->zero`` and ``descr->one`` constants have been replaced with - function calls, ``PyArray_Zero``, and ``PyArray_One`` (be sure to read the - code and free the resulting memory if you use these calls). - -* If you passed ``array->dimensions`` and ``array->strides`` around - to functions, you will need to fix some code. These are now - ``npy_intp*`` pointers. On 32-bit systems there won't be a problem. - However, on 64-bit systems, you will need to make changes to avoid - errors and segfaults. - - -The header files ``arrayobject.h`` and ``ufuncobject.h`` contain many defines -that you may find useful. The files ``__ufunc_api.h`` and -``__multiarray_api.h`` contain the available C-API function calls with -their function signatures. - -All of these headers are installed to -``<YOUR_PYTHON_LOCATION>/site-packages/numpy/core/include`` - - -Getting arrays in C-code -========================= - -All new arrays can be created using ``PyArray_NewFromDescr``. A simple interface -equivalent to ``PyArray_FromDims`` is ``PyArray_SimpleNew(nd, dims, typenum)`` -and to ``PyArray_FromDimsAndData`` is -``PyArray_SimpleNewFromData(nd, dims, typenum, data)``. - -This is a very flexible function. - -:: - - PyObject * PyArray_NewFromDescr(PyTypeObject *subtype, PyArray_Descr *descr, - int nd, npy_intp *dims, - npy_intp *strides, char *data, - int flags, PyObject *obj); - -``subtype`` : ``PyTypeObject *`` - The subtype that should be created (either pass in - ``&PyArray_Type``, or ``obj->ob_type``, - where ``obj`` is an instance of a subtype (or subclass) of - ``PyArray_Type``). - -``descr`` : ``PyArray_Descr *`` - The type descriptor for the array. This is a Python object (this - function steals a reference to it). The easiest way to get one is - using ``PyArray_DescrFromType(<typenum>)``. If you want to use a - flexible size array, then you need to use - ``PyArray_DescrNewFromType(<flexible typenum>)`` and set its ``elsize`` - parameter to the desired size. The typenum in both of these cases - is one of the ``PyArray_XXXX`` enumerated types. - -``nd`` : ``int`` - The number of dimensions (<``MAX_DIMS``) - -``*dims`` : ``npy_intp *`` - A pointer to the size in each dimension. Information will be - copied from here. - -``*strides`` : ``npy_intp *`` - The strides this array should have. For new arrays created by this - routine, this should be ``NULL``. If you pass in memory for this array - to use, then you can pass in the strides information as well - (otherwise it will be created for you and default to C-contiguous - or Fortran contiguous). Any strides will be copied into the array - structure. Do not pass in bad strides information!!!! - - ``PyArray_CheckStrides(...)`` can help but you must call it if you are - unsure. You cannot pass in strides information when data is ``NULL`` - and this routine is creating its own memory. - -``*data`` : ``char *`` - ``NULL`` for creating brand-new memory. If you want this array to wrap - another memory area, then pass the pointer here. You are - responsible for deleting the memory in that case, but do not do so - until the new array object has been deleted. The best way to - handle that is to get the memory from another Python object, - ``INCREF`` that Python object after passing it's data pointer to this - routine, and set the ``->base`` member of the returned array to the - Python object. *You are responsible for* setting ``PyArray_BASE(ret)`` - to the base object. Failure to do so will create a memory leak. - - If you pass in a data buffer, the ``flags`` argument will be the flags - of the new array. If you create a new array, a non-zero flags - argument indicates that you want the array to be in Fortran order. - -``flags`` : ``int`` - Either the flags showing how to interpret the data buffer passed - in, or if a new array is created, nonzero to indicate a Fortran - order array. See below for an explanation of the flags. - -``obj`` : ``PyObject *`` - If subtypes is ``&PyArray_Type``, this argument is - ignored. Otherwise, the ``__array_finalize__`` method of the subtype - is called (if present) and passed this object. This is usually an - array of the type to be created (so the ``__array_finalize__`` method - must handle an array argument. But, it can be anything...) - -Note: The returned array object will be uninitialized unless the type is -``PyArray_OBJECT`` in which case the memory will be set to ``NULL``. - -``PyArray_SimpleNew(nd, dims, typenum)`` is a drop-in replacement for -``PyArray_FromDims`` (except it takes ``npy_intp*`` dims instead of ``int*`` dims -which matters on 64-bit systems) and it does not initialize the memory -to zero. - -``PyArray_SimpleNew`` is just a macro for ``PyArray_New`` with default arguments. -Use ``PyArray_FILLWBYTE(arr, 0)`` to fill with zeros. - -The ``PyArray_FromDims`` and family of functions are still available and -are loose wrappers around this function. These functions still take -``int *`` arguments. This should be fine on 32-bit systems, but on 64-bit -systems you may run into trouble if you frequently passed -``PyArray_FromDims`` the dimensions member of the old ``PyArrayObject`` structure -because ``sizeof(npy_intp) != sizeof(int)``. - - -Getting an arrayobject from an arbitrary Python object -====================================================== - -``PyArray_FromAny(...)`` - -This function replaces ``PyArray_ContiguousFromObject`` and friends (those -function calls still remain but they are loose wrappers around the -``PyArray_FromAny`` call). - -:: - - static PyObject * - PyArray_FromAny(PyObject *op, PyArray_Descr *dtype, int min_depth, - int max_depth, int requires, PyObject *context) - - -``op`` : ``PyObject *`` - The Python object to "convert" to an array object - -``dtype`` : ``PyArray_Descr *`` - The desired data-type descriptor. This can be ``NULL``, if the - descriptor should be determined by the object. Unless ``FORCECAST`` is - present in ``flags``, this call will generate an error if the data - type cannot be safely obtained from the object. - -``min_depth`` : ``int`` - The minimum depth of array needed or 0 if doesn't matter - -``max_depth`` : ``int`` - The maximum depth of array allowed or 0 if doesn't matter - -``requires`` : ``int`` - A flag indicating the "requirements" of the returned array. These - are the usual ndarray flags (see `NDArray flags`_ below). In - addition, there are three flags used only for the ``FromAny`` - family of functions: - - - ``ENSURECOPY``: always copy the array. Returned arrays always - have ``CONTIGUOUS``, ``ALIGNED``, and ``WRITEABLE`` set. - - ``ENSUREARRAY``: ensure the returned array is an ndarray. - - ``FORCECAST``: cause a cast to occur regardless of whether or - not it is safe. - -``context`` : ``PyObject *`` - If the Python object ``op`` is not a numpy array, but has an - ``__array__`` method, context is passed as the second argument to - that method (the first is the typecode). Almost always this - parameter is ``NULL``. - - -``PyArray_ContiguousFromAny(op, typenum, min_depth, max_depth)`` is -equivalent to ``PyArray_ContiguousFromObject(...)`` (which is still -available), except it will return the subclass if op is already a -subclass of the ndarray. The ``ContiguousFromObject`` version will -always return an ndarray. - -Passing Data Type information to C-code -======================================= - -All datatypes are handled using the ``PyArray_Descr *`` structure. -This structure can be obtained from a Python object using -``PyArray_DescrConverter`` and ``PyArray_DescrConverter2``. The former -returns the default ``PyArray_LONG`` descriptor when the input object -is None, while the latter returns ``NULL`` when the input object is ``None``. - -See the ``arraymethods.c`` and ``multiarraymodule.c`` files for many -examples of usage. - -Getting at the structure of the array. --------------------------------------- - -You should use the ``#defines`` provided to access array structure portions: - -- ``PyArray_DATA(obj)`` : returns a ``void *`` to the array data -- ``PyArray_BYTES(obj)`` : return a ``char *`` to the array data -- ``PyArray_ITEMSIZE(obj)`` -- ``PyArray_NDIM(obj)`` -- ``PyArray_DIMS(obj)`` -- ``PyArray_DIM(obj, n)`` -- ``PyArray_STRIDES(obj)`` -- ``PyArray_STRIDE(obj,n)`` -- ``PyArray_DESCR(obj)`` -- ``PyArray_BASE(obj)`` - -see more in ``arrayobject.h`` - - -NDArray Flags -============= - -The ``flags`` attribute of the ``PyArrayObject`` structure contains important -information about the memory used by the array (pointed to by the data member) -This flags information must be kept accurate or strange results and even -segfaults may result. - -There are 6 (binary) flags that describe the memory area used by the -data buffer. These constants are defined in ``arrayobject.h`` and -determine the bit-position of the flag. Python exposes a nice attribute- -based interface as well as a dictionary-like interface for getting -(and, if appropriate, setting) these flags. - -Memory areas of all kinds can be pointed to by an ndarray, necessitating -these flags. If you get an arbitrary ``PyArrayObject`` in C-code, -you need to be aware of the flags that are set. -If you need to guarantee a certain kind of array -(like ``NPY_CONTIGUOUS`` and ``NPY_BEHAVED``), then pass these requirements into the -PyArray_FromAny function. - - -``NPY_CONTIGUOUS`` - True if the array is (C-style) contiguous in memory. -``NPY_FORTRAN`` - True if the array is (Fortran-style) contiguous in memory. - -Notice that contiguous 1-d arrays are always both ``NPY_FORTRAN`` contiguous -and C contiguous. Both of these flags can be checked and are convenience -flags only as whether or not an array is ``NPY_CONTIGUOUS`` or ``NPY_FORTRAN`` -can be determined by the ``strides``, ``dimensions``, and ``itemsize`` -attributes. - -``NPY_OWNDATA`` - True if the array owns the memory (it will try and free it using - ``PyDataMem_FREE()`` on deallocation --- so it better really own it). - -These three flags facilitate using a data pointer that is a memory-mapped -array, or part of some larger record array. But, they may have other uses... - -``NPY_ALIGNED`` - True if the data buffer is aligned for the type and the strides - are multiples of the alignment factor as well. This can be - checked. - -``NPY_WRITEABLE`` - True only if the data buffer can be "written" to. - -``NPY_WRITEBACKIFCOPY`` - This is a special flag that is set if this array represents a copy - made because a user required certain flags in ``PyArray_FromAny`` and - a copy had to be made of some other array (and the user asked for - this flag to be set in such a situation). The base attribute then - points to the "misbehaved" array (which is set read_only). If you use - this flag, you are must call ``PyArray_ResolveWritebackIfCopy`` before - deallocating this array (i.e. before calling ``Py_DECREF`` the last time) - which will write the data contents back to the "misbehaved" array (casting - if necessary) and will reset the "misbehaved" array to ``WRITEABLE``. If - the "misbehaved" array was not ``WRITEABLE`` to begin with then - ``PyArray_FromAny`` would have returned an error because ``WRITEBACKIFCOPY`` - would not have been possible. In error conditions, call - ``PyArray_DiscardWritebackIfCopy`` to throw away the scratch buffer, then - ``Py_DECREF`` or ``Py_XDECREF``. - -``NPY_UPDATEIFCOPY`` - Similar to ``NPY_WRITEBACKIFCOPY``, but deprecated since it copied the - contents back when the array is deallocated, which is not explicit and - relies on refcount semantics. Refcount semantics are unreliable on - alternative implementations of python such as PyPy. - -``PyArray_UpdateFlags(obj, flags)`` will update the ``obj->flags`` for -``flags`` which can be any of ``NPY_CONTIGUOUS``, ``NPY_FORTRAN``, ``NPY_ALIGNED``, or -``NPY_WRITEABLE``. - -Some useful combinations of these flags: - -- ``NPY_BEHAVED = NPY_ALIGNED | NPY_WRITEABLE`` -- ``NPY_CARRAY = NPY_DEFAULT = NPY_CONTIGUOUS | NPY_BEHAVED`` -- ``NPY_CARRAY_RO = NPY_CONTIGUOUS | NPY_ALIGNED`` -- ``NPY_FARRAY = NPY_FORTRAN | NPY_BEHAVED`` -- ``NPY_FARRAY_RO = NPY_FORTRAN | NPY_ALIGNED`` - -The macro ``PyArray_CHECKFLAGS(obj, flags)`` can test any combination of flags. -There are several default combinations defined as macros already -(see ``arrayobject.h``) - -In particular, there are ``ISBEHAVED``, ``ISBEHAVED_RO``, ``ISCARRAY`` -and ``ISFARRAY`` macros that also check to make sure the array is in -native byte order (as determined) by the data-type descriptor. - -There are more C-API enhancements which you can discover in the code, -or buy the book (http://www.trelgol.com) |