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"""
============================
``ctypes`` Utility Functions
============================
See Also
--------
load_library : Load a C library.
ndpointer : Array restype/argtype with verification.
as_ctypes : Create a ctypes array from an ndarray.
as_array : Create an ndarray from a ctypes array.
References
----------
.. [1] "SciPy Cookbook: ctypes", https://scipy-cookbook.readthedocs.io/items/Ctypes.html
Examples
--------
Load the C library:
>>> _lib = np.ctypeslib.load_library('libmystuff', '.') #doctest: +SKIP
Our result type, an ndarray that must be of type double, be 1-dimensional
and is C-contiguous in memory:
>>> array_1d_double = np.ctypeslib.ndpointer(
... dtype=np.double,
... ndim=1, flags='CONTIGUOUS') #doctest: +SKIP
Our C-function typically takes an array and updates its values
in-place. For example::
void foo_func(double* x, int length)
{
int i;
for (i = 0; i < length; i++) {
x[i] = i*i;
}
}
We wrap it using:
>>> _lib.foo_func.restype = None #doctest: +SKIP
>>> _lib.foo_func.argtypes = [array_1d_double, c_int] #doctest: +SKIP
Then, we're ready to call ``foo_func``:
>>> out = np.empty(15, dtype=np.double)
>>> _lib.foo_func(out, len(out)) #doctest: +SKIP
"""
__all__ = ['load_library', 'ndpointer', 'c_intp', 'as_ctypes', 'as_array',
'as_ctypes_type']
import os
from numpy import (
integer, ndarray, dtype as _dtype, asarray, frombuffer
)
from numpy.core.multiarray import _flagdict, flagsobj
try:
import ctypes
except ImportError:
ctypes = None
if ctypes is None:
def _dummy(*args, **kwds):
"""
Dummy object that raises an ImportError if ctypes is not available.
Raises
------
ImportError
If ctypes is not available.
"""
raise ImportError("ctypes is not available.")
load_library = _dummy
as_ctypes = _dummy
as_array = _dummy
from numpy import intp as c_intp
_ndptr_base = object
else:
import numpy.core._internal as nic
c_intp = nic._getintp_ctype()
del nic
_ndptr_base = ctypes.c_void_p
# Adapted from Albert Strasheim
def load_library(libname, loader_path):
"""
It is possible to load a library using
>>> lib = ctypes.cdll[<full_path_name>] # doctest: +SKIP
But there are cross-platform considerations, such as library file extensions,
plus the fact Windows will just load the first library it finds with that name.
NumPy supplies the load_library function as a convenience.
.. versionchanged:: 1.20.0
Allow libname and loader_path to take any
:term:`python:path-like object`.
Parameters
----------
libname : path-like
Name of the library, which can have 'lib' as a prefix,
but without an extension.
loader_path : path-like
Where the library can be found.
Returns
-------
ctypes.cdll[libpath] : library object
A ctypes library object
Raises
------
OSError
If there is no library with the expected extension, or the
library is defective and cannot be loaded.
"""
# Convert path-like objects into strings
libname = os.fsdecode(libname)
loader_path = os.fsdecode(loader_path)
ext = os.path.splitext(libname)[1]
if not ext:
import sys
import sysconfig
# Try to load library with platform-specific name, otherwise
# default to libname.[so|dll|dylib]. Sometimes, these files are
# built erroneously on non-linux platforms.
base_ext = ".so"
if sys.platform.startswith("darwin"):
base_ext = ".dylib"
elif sys.platform.startswith("win"):
base_ext = ".dll"
libname_ext = [libname + base_ext]
so_ext = sysconfig.get_config_var("EXT_SUFFIX")
if not so_ext == base_ext:
libname_ext.insert(0, libname + so_ext)
else:
libname_ext = [libname]
loader_path = os.path.abspath(loader_path)
if not os.path.isdir(loader_path):
libdir = os.path.dirname(loader_path)
else:
libdir = loader_path
for ln in libname_ext:
libpath = os.path.join(libdir, ln)
if os.path.exists(libpath):
try:
return ctypes.cdll[libpath]
except OSError:
## defective lib file
raise
## if no successful return in the libname_ext loop:
raise OSError("no file with expected extension")
def _num_fromflags(flaglist):
num = 0
for val in flaglist:
num += _flagdict[val]
return num
_flagnames = ['C_CONTIGUOUS', 'F_CONTIGUOUS', 'ALIGNED', 'WRITEABLE',
'OWNDATA', 'WRITEBACKIFCOPY']
def _flags_fromnum(num):
res = []
for key in _flagnames:
value = _flagdict[key]
if (num & value):
res.append(key)
return res
class _ndptr(_ndptr_base):
@classmethod
def from_param(cls, obj):
if not isinstance(obj, ndarray):
raise TypeError("argument must be an ndarray")
if cls._dtype_ is not None \
and obj.dtype != cls._dtype_:
raise TypeError("array must have data type %s" % cls._dtype_)
if cls._ndim_ is not None \
and obj.ndim != cls._ndim_:
raise TypeError("array must have %d dimension(s)" % cls._ndim_)
if cls._shape_ is not None \
and obj.shape != cls._shape_:
raise TypeError("array must have shape %s" % str(cls._shape_))
if cls._flags_ is not None \
and ((obj.flags.num & cls._flags_) != cls._flags_):
raise TypeError("array must have flags %s" %
_flags_fromnum(cls._flags_))
return obj.ctypes
class _concrete_ndptr(_ndptr):
"""
Like _ndptr, but with `_shape_` and `_dtype_` specified.
Notably, this means the pointer has enough information to reconstruct
the array, which is not generally true.
"""
def _check_retval_(self):
"""
This method is called when this class is used as the .restype
attribute for a shared-library function, to automatically wrap the
pointer into an array.
"""
return self.contents
@property
def contents(self):
"""
Get an ndarray viewing the data pointed to by this pointer.
This mirrors the `contents` attribute of a normal ctypes pointer
"""
full_dtype = _dtype((self._dtype_, self._shape_))
full_ctype = ctypes.c_char * full_dtype.itemsize
buffer = ctypes.cast(self, ctypes.POINTER(full_ctype)).contents
return frombuffer(buffer, dtype=full_dtype).squeeze(axis=0)
# Factory for an array-checking class with from_param defined for
# use with ctypes argtypes mechanism
_pointer_type_cache = {}
def ndpointer(dtype=None, ndim=None, shape=None, flags=None):
"""
Array-checking restype/argtypes.
An ndpointer instance is used to describe an ndarray in restypes
and argtypes specifications. This approach is more flexible than
using, for example, ``POINTER(c_double)``, since several restrictions
can be specified, which are verified upon calling the ctypes function.
These include data type, number of dimensions, shape and flags. If a
given array does not satisfy the specified restrictions,
a ``TypeError`` is raised.
Parameters
----------
dtype : data-type, optional
Array data-type.
ndim : int, optional
Number of array dimensions.
shape : tuple of ints, optional
Array shape.
flags : str or tuple of str
Array flags; may be one or more of:
- C_CONTIGUOUS / C / CONTIGUOUS
- F_CONTIGUOUS / F / FORTRAN
- OWNDATA / O
- WRITEABLE / W
- ALIGNED / A
- WRITEBACKIFCOPY / X
Returns
-------
klass : ndpointer type object
A type object, which is an ``_ndtpr`` instance containing
dtype, ndim, shape and flags information.
Raises
------
TypeError
If a given array does not satisfy the specified restrictions.
Examples
--------
>>> clib.somefunc.argtypes = [np.ctypeslib.ndpointer(dtype=np.float64,
... ndim=1,
... flags='C_CONTIGUOUS')]
... #doctest: +SKIP
>>> clib.somefunc(np.array([1, 2, 3], dtype=np.float64))
... #doctest: +SKIP
"""
# normalize dtype to an Optional[dtype]
if dtype is not None:
dtype = _dtype(dtype)
# normalize flags to an Optional[int]
num = None
if flags is not None:
if isinstance(flags, str):
flags = flags.split(',')
elif isinstance(flags, (int, integer)):
num = flags
flags = _flags_fromnum(num)
elif isinstance(flags, flagsobj):
num = flags.num
flags = _flags_fromnum(num)
if num is None:
try:
flags = [x.strip().upper() for x in flags]
except Exception as e:
raise TypeError("invalid flags specification") from e
num = _num_fromflags(flags)
# normalize shape to an Optional[tuple]
if shape is not None:
try:
shape = tuple(shape)
except TypeError:
# single integer -> 1-tuple
shape = (shape,)
cache_key = (dtype, ndim, shape, num)
try:
return _pointer_type_cache[cache_key]
except KeyError:
pass
# produce a name for the new type
if dtype is None:
name = 'any'
elif dtype.names is not None:
name = str(id(dtype))
else:
name = dtype.str
if ndim is not None:
name += "_%dd" % ndim
if shape is not None:
name += "_"+"x".join(str(x) for x in shape)
if flags is not None:
name += "_"+"_".join(flags)
if dtype is not None and shape is not None:
base = _concrete_ndptr
else:
base = _ndptr
klass = type("ndpointer_%s"%name, (base,),
{"_dtype_": dtype,
"_shape_" : shape,
"_ndim_" : ndim,
"_flags_" : num})
_pointer_type_cache[cache_key] = klass
return klass
if ctypes is not None:
def _ctype_ndarray(element_type, shape):
""" Create an ndarray of the given element type and shape """
for dim in shape[::-1]:
element_type = dim * element_type
# prevent the type name include np.ctypeslib
element_type.__module__ = None
return element_type
def _get_scalar_type_map():
"""
Return a dictionary mapping native endian scalar dtype to ctypes types
"""
ct = ctypes
simple_types = [
ct.c_byte, ct.c_short, ct.c_int, ct.c_long, ct.c_longlong,
ct.c_ubyte, ct.c_ushort, ct.c_uint, ct.c_ulong, ct.c_ulonglong,
ct.c_float, ct.c_double,
ct.c_bool,
]
return {_dtype(ctype): ctype for ctype in simple_types}
_scalar_type_map = _get_scalar_type_map()
def _ctype_from_dtype_scalar(dtype):
# swapping twice ensure that `=` is promoted to <, >, or |
dtype_with_endian = dtype.newbyteorder('S').newbyteorder('S')
dtype_native = dtype.newbyteorder('=')
try:
ctype = _scalar_type_map[dtype_native]
except KeyError as e:
raise NotImplementedError(
"Converting {!r} to a ctypes type".format(dtype)
) from None
if dtype_with_endian.byteorder == '>':
ctype = ctype.__ctype_be__
elif dtype_with_endian.byteorder == '<':
ctype = ctype.__ctype_le__
return ctype
def _ctype_from_dtype_subarray(dtype):
element_dtype, shape = dtype.subdtype
ctype = _ctype_from_dtype(element_dtype)
return _ctype_ndarray(ctype, shape)
def _ctype_from_dtype_structured(dtype):
# extract offsets of each field
field_data = []
for name in dtype.names:
field_dtype, offset = dtype.fields[name][:2]
field_data.append((offset, name, _ctype_from_dtype(field_dtype)))
# ctypes doesn't care about field order
field_data = sorted(field_data, key=lambda f: f[0])
if len(field_data) > 1 and all(offset == 0 for offset, name, ctype in field_data):
# union, if multiple fields all at address 0
size = 0
_fields_ = []
for offset, name, ctype in field_data:
_fields_.append((name, ctype))
size = max(size, ctypes.sizeof(ctype))
# pad to the right size
if dtype.itemsize != size:
_fields_.append(('', ctypes.c_char * dtype.itemsize))
# we inserted manual padding, so always `_pack_`
return type('union', (ctypes.Union,), dict(
_fields_=_fields_,
_pack_=1,
__module__=None,
))
else:
last_offset = 0
_fields_ = []
for offset, name, ctype in field_data:
padding = offset - last_offset
if padding < 0:
raise NotImplementedError("Overlapping fields")
if padding > 0:
_fields_.append(('', ctypes.c_char * padding))
_fields_.append((name, ctype))
last_offset = offset + ctypes.sizeof(ctype)
padding = dtype.itemsize - last_offset
if padding > 0:
_fields_.append(('', ctypes.c_char * padding))
# we inserted manual padding, so always `_pack_`
return type('struct', (ctypes.Structure,), dict(
_fields_=_fields_,
_pack_=1,
__module__=None,
))
def _ctype_from_dtype(dtype):
if dtype.fields is not None:
return _ctype_from_dtype_structured(dtype)
elif dtype.subdtype is not None:
return _ctype_from_dtype_subarray(dtype)
else:
return _ctype_from_dtype_scalar(dtype)
def as_ctypes_type(dtype):
r"""
Convert a dtype into a ctypes type.
Parameters
----------
dtype : dtype
The dtype to convert
Returns
-------
ctype
A ctype scalar, union, array, or struct
Raises
------
NotImplementedError
If the conversion is not possible
Notes
-----
This function does not losslessly round-trip in either direction.
``np.dtype(as_ctypes_type(dt))`` will:
- insert padding fields
- reorder fields to be sorted by offset
- discard field titles
``as_ctypes_type(np.dtype(ctype))`` will:
- discard the class names of `ctypes.Structure`\ s and
`ctypes.Union`\ s
- convert single-element `ctypes.Union`\ s into single-element
`ctypes.Structure`\ s
- insert padding fields
"""
return _ctype_from_dtype(_dtype(dtype))
def as_array(obj, shape=None):
"""
Create a numpy array from a ctypes array or POINTER.
The numpy array shares the memory with the ctypes object.
The shape parameter must be given if converting from a ctypes POINTER.
The shape parameter is ignored if converting from a ctypes array
"""
if isinstance(obj, ctypes._Pointer):
# convert pointers to an array of the desired shape
if shape is None:
raise TypeError(
'as_array() requires a shape argument when called on a '
'pointer')
p_arr_type = ctypes.POINTER(_ctype_ndarray(obj._type_, shape))
obj = ctypes.cast(obj, p_arr_type).contents
return asarray(obj)
def as_ctypes(obj):
"""Create and return a ctypes object from a numpy array. Actually
anything that exposes the __array_interface__ is accepted."""
ai = obj.__array_interface__
if ai["strides"]:
raise TypeError("strided arrays not supported")
if ai["version"] != 3:
raise TypeError("only __array_interface__ version 3 supported")
addr, readonly = ai["data"]
if readonly:
raise TypeError("readonly arrays unsupported")
# can't use `_dtype((ai["typestr"], ai["shape"]))` here, as it overflows
# dtype.itemsize (gh-14214)
ctype_scalar = as_ctypes_type(ai["typestr"])
result_type = _ctype_ndarray(ctype_scalar, ai["shape"])
result = result_type.from_address(addr)
result.__keep = obj
return result