Python与C语言混合编程：通过通过ctypes.cdll加载python扩展组件

迈不过友情╰ 2022-03-22 08:44 254阅读 0赞

通过ctypes扩展python组件可能是最简单的python扩展了。

## 源码 ##

Makefile

osx:
    	gcc -shared -undefined dynamic_lookup sample.c -o libsample.so
    
    linux:
    	gcc -g -Wall -shared -fPIC sample.c -o libsample.so

因为我使用的是Ubuntu18.04，所以直接在dev目录下输入命令  
$ make linux  
即可得到libsample.so，如果要在sub01目录下使用，则需要把该文件拷贝到sub01目录下去。

sample.py

# sample.py
    import ctypes
    import os
    from ctypes import util, cdll
    # .so file is located in the directory above. See Makefile for
    # build instructions
    #_path = '../libsample.so'
    test_path = util.find_library('/home/matthew/dev/libsample.so')
    
    prev_path = ctypes.util.find_library('../libsample.so')
    dir_path = os.path.dirname(os.path.realpath(__file__)) + '/libsample.so'
    
    _mod = ctypes.cdll.LoadLibrary(dir_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

## 如何使用 ##

在sub01目录下，就可以这样使用了，

$ python
    >>>import sample
    >>>print(sample.gcd(35,42))
    
    下面相同，都是测试代码，请自行验证
    print( sample.in_mandel(0,0,500))
    print( sample.in_mandel(2.0,1.0,500))
    print( sample.divide(42,8) )
    print( sample.avg([1,2,3]) )
    p1 = sample.Point(1,2) 
    p2 = sample.Point(4,5) 
    print(p1 )
    print(p2 )
    print( sample.distance(p1,p2) )

## 说明 ##

这里要注意，在sample.py中，通过ctypes.cdll加载组件时，我使用了三个路径，如果你的libsample.so在dev目录下，则应该使用prev\_path；如果你和我一样，把libsample.so拷贝到了sub01目录下面，那么就可以使用dir\_path,  
\_mod = ctypes.cdll.LoadLibrary(dir\_path)

函数的数据类型必须说明，例如

gcd = \_mod.gcd                                            \#表示最大公约数函数gcd  
gcd.argtypes = (ctypes.c\_int, ctypes.c\_int)   \#gcd 输入函数的数据类型  
gcd.restype = ctypes.c\_int                            \#gcd 输出函数的数据类型

[https_blog.csdn.net_tanmx219_article_details_86665706]: https://blog.csdn.net/tanmx219/article/details/86665706