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Add a few comments throughout numpy.h

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This commit is contained in:
Ivan Smirnov 2016-06-29 15:21:51 +01:00
parent 2f01f01866
commit 3b803846d5
1 changed files with 20 additions and 5 deletions
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25
include/pybind11/numpy.h
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@ -123,20 +123,29 @@ public:
PyObject *arr = nullptr, *descr = nullptr;
int ndim = 0;
Py_ssize_t dims[32];
API& api = lookup_api();
// allocate zeroed memory if it hasn't been provided
// Allocate zeroed memory if it hasn't been provided by the caller.
// Normally, we could leave this null for NumPy to allocate memory for us, but
// since we need a memoryview, the data pointer has to be non-null. NumPy uses
// malloc if NPY_NEEDS_INIT is not set (in which case it uses calloc); however,
// we don't have a descriptor yet (only a buffer format string), so we can't
// access the flags. The safest thing to do is thus to use calloc.
auto buf_info = info;
if (!buf_info.ptr)
// always allocate at least 1 element, same way as NumPy does it
buf_info.ptr = std::calloc(std::max(info.size, 1ul), info.itemsize);
if (!buf_info.ptr)
pybind11_fail("NumPy: failed to allocate memory for buffer");
auto view = memoryview(buf_info);
API& api = lookup_api();
// PyArray_GetArrayParamsFromObject seems to be the only low-level API function
// that will accept arbitrary buffers (including structured types)
auto view = memoryview(buf_info);
auto res = api.PyArray_GetArrayParamsFromObject_(view.ptr(), nullptr, 1, &descr,
&ndim, dims, &arr, nullptr);
if (res < 0 || !arr || descr)
// We expect arr to have a pointer to a newly created array, in which case all
// other parameters like descr would be set to null, according to the API.
pybind11_fail("NumPy: unable to convert buffer to an array");
m_ptr = arr;
}
@ -161,7 +170,8 @@ public:
return nullptr;
API &api = lookup_api();
PyObject *descr = detail::npy_format_descriptor<T>::dtype().release().ptr();
PyObject *result = api.PyArray_FromAny_(ptr, descr, 0, 0, API::NPY_ENSURE_ARRAY_ | ExtraFlags, nullptr);
PyObject *result = api.PyArray_FromAny_(ptr, descr, 0, 0,
API::NPY_ENSURE_ARRAY_ | ExtraFlags, nullptr);
if (!result)
PyErr_Clear();
Py_DECREF(ptr);
@ -254,8 +264,11 @@ struct npy_format_descriptor<T, typename std::enable_if<is_pod_struct<T>::value>
args["names"] = names;
args["offsets"] = offsets;
args["formats"] = formats;
// This is essentially the same as calling np.dtype() constructor in Python and passing
// it a dict of the form {'names': ..., 'formats': ..., 'offsets': ...}.
if (!api.PyArray_DescrConverter_(args.release().ptr(), &dtype_()) || !dtype_())
pybind11_fail("NumPy: failed to create structured dtype");
// Let NumPy figure the buffer format string for us: memoryview(np.empty(0, dtype)).format
auto np = module::import("numpy");
auto empty = (object) np.attr("empty");
if (auto arr = (object) empty(int_(0), dtype())) {
@ -274,6 +287,7 @@ private:
static inline char* format_() { static char s[4096]; return s; }
};
// Extract name, offset and format descriptor for a struct field
#define PYBIND11_FIELD_DESCRIPTOR(Type, Field) \
::pybind11::detail::field_descriptor { \
#Field, offsetof(Type, Field), \
@ -295,7 +309,7 @@ private:
#define PYBIND11_MAP_NEXT0(test, next, ...) next PYBIND11_MAP_OUT
#define PYBIND11_MAP_NEXT1(test, next) PYBIND11_MAP_NEXT0 (test, next, 0)
#define PYBIND11_MAP_NEXT(test, next) PYBIND11_MAP_NEXT1 (PYBIND11_MAP_GET_END test, next)
#ifdef _MSC_VER // MSVC is not as eager to expand macros
#ifdef _MSC_VER // MSVC is not as eager to expand macros, hence this workaround
#define PYBIND11_MAP_LIST_NEXT1(test, next) \
PYBIND11_EVAL0 (PYBIND11_MAP_NEXT0 (test, PYBIND11_MAP_COMMA next, 0))
#else
@ -308,6 +322,7 @@ private:
f(t, x) PYBIND11_MAP_LIST_NEXT (peek, PYBIND11_MAP_LIST1) (f, t, peek, __VA_ARGS__)
#define PYBIND11_MAP_LIST1(f, t, x, peek, ...) \
f(t, x) PYBIND11_MAP_LIST_NEXT (peek, PYBIND11_MAP_LIST0) (f, t, peek, __VA_ARGS__)
// PYBIND11_MAP_LIST(f, t, a1, a2, ...) expands to f(t, a1), f(t, a2), ...
#define PYBIND11_MAP_LIST(f, t, ...) \
PYBIND11_EVAL (PYBIND11_MAP_LIST1 (f, t, __VA_ARGS__, (), 0))