使用ctypes访问C代码

可以参考这篇文章： https://www.baidu.com/link?url=6djl4oF9q-bjXsKIc7n5xA5eoO3YbD_ISURCaytWx9o0B2dmmEhXclgxb_R

对于需要调用C代码的一些小的问题，通常使用Python标准库中的 ctypes 模块就足够了。 要使用 ctypes ，你首先要确保你要访问的C代码已经被编译到和Python解释器兼容 （同样的架构、字大小、编译器等）的某个共享库中了。 为了进行本节的演示，假设你有一个共享库名字叫 libsample.so ，里面的内容就是15章介绍部分那样。 另外还假设这个 libsample.so 文件被放置到位于 sample.py 文件相同的目录中了。

要访问这个函数库，你要先构建一个包装它的Python模块，如下这样：

# sample.py
import ctypes
import os

# Try to locate the .so file in the same directory as this file
_file = 'libsample.so'
_path = os.path.join(*(os.path.split(__file__)[:-1] + (_file,)))
_mod = ctypes.cdll.LoadLibrary(_path)

# int gcd(int, int)
gcd = _mod.gcd
gcd.argtypes = (ctypes.c_int, ctypes.c_int)
gcd.restype = ctypes.c_int

# int in_mandel(double, double, int)
in_mandel = _mod.in_mandel
in_mandel.argtypes = (ctypes.c_double, ctypes.c_double, ctypes.c_int)
in_mandel.restype = ctypes.c_int

# int divide(int, int, int *)
_divide = _mod.divide
_divide.argtypes = (ctypes.c_int, ctypes.c_int, ctypes.POINTER(ctypes.c_int))
_divide.restype = ctypes.c_int

def divide(x, y):
    rem = ctypes.c_int()
    quot = _divide(x, y, rem)

    return quot,rem.value

# void avg(double *, int n)
# Define a special type for the 'double *' argument
class DoubleArrayType:
    def from_param(self, param):
        typename = type(param).__name__
        if hasattr(self, 'from_' + typename):
            return getattr(self, 'from_' + typename)(param)
        elif isinstance(param, ctypes.Array):
            return param
        else:
            raise TypeError("Can't convert %s" % typename)

    # Cast from array.array objects
    def from_array(self, param):
        if param.typecode != 'd':
            raise TypeError('must be an array of doubles')
        ptr, _ = param.buffer_info()
        return ctypes.cast(ptr, ctypes.POINTER(ctypes.c_double))

    # Cast from lists/tuples
    def from_list(self, param):
        val = ((ctypes.c_double)*len(param))(*param)
        return val

    from_tuple = from_list

    # Cast from a numpy array
    def from_ndarray(self, param):
        return param.ctypes.data_as(ctypes.POINTER(ctypes.c_double))

DoubleArray = DoubleArrayType()
_avg = _mod.avg
_avg.argtypes = (DoubleArray, ctypes.c_int)
_avg.restype = ctypes.c_double

def avg(values):
    return _avg(values, len(values))

# struct Point { }
class Point(ctypes.Structure):
    _fields_ = [('x', ctypes.c_double),
                ('y', ctypes.c_double)]

# double distance(Point *, Point *)
distance = _mod.distance
distance.argtypes = (ctypes.POINTER(Point), ctypes.POINTER(Point))
distance.restype = ctypes.c_double
如果一切正常，你就可以加载并使用里面定义的C函数了。例如：

>>> import sample
>>> sample.gcd(35,42)
7
>>> sample.in_mandel(0,0,500)
1
>>> sample.in_mandel(2.0,1.0,500)
0
>>> sample.divide(42,8)
(5, 2)
>>> sample.avg([1,2,3])
2.0
>>> p1 = sample.Point(1,2)
>>> p2 = sample.Point(4,5)
>>> sample.distance(p1,p2)
4.242640687119285
>>>