The distutils documentation here states that: A C extension for CPython is a shared library (e.g. a .so file on Linux, .pyd on Windows), which exports an initialization function. So the only difference regarding a plain shared library seems to be the initialization function (besides a sensible file naming convention I don’t think you have … Read more
You have to keep a reference to your Wrapper while any numpy array exists. Easiest way to achieve this, is to save this reference in a attribute of the ctype-buffer: class MyWrapper(object): def __init__(self, n=10): # buffer allocated by external library self.size = n self.addr = libc.malloc(C.sizeof(C.c_int) * n) def __del__(self): # buffer freed by … Read more
You can use os.path.dirname(__file__) to get the directory where the Python source file is located.
You should call C from Python by writing a ctypes wrapper. Cython is for making python-like code run faster, ctypes is for making C functions callable from python. What you need to do is the following: Write the C functions you want to use. (You probably did this already) Create a shared object (.so, for … Read more
Thanks to Eryksun the solution: Python code string1 = “my string 1” string2 = “my string 2” # create byte objects from the strings b_string1 = string1.encode(‘utf-8’) b_string2 = string2.encode(‘utf-8’) # send strings to c function my_c_function.argtypes = [ctypes.c_char_p, ctypes.char_p] my_c_function(b_string1, b_string2)
>>> ctypes.c_long(1).value 1
Those extra ‘1’s at the end of each number are the return value from printf, which returns the number of chars that it prints. The return value of a function called in the interactive interpreter is automatically printed (unless it’s None). In fact, the interactive interpreter prints any non-None expression that isn’t assigned. And of … Read more
Creating NumPy arrays from a ctypes pointer object is a problematic operation. It is unclear who actually owns the memory the pointer is pointing to. When will it be freed again? How long is it valid? Whenever possible I would try to avoid this kind of construct. It is so much easier and safer to … Read more
Have a look at ctypes.string_at. Here’s an example. It dumps the raw data structure of a CPython integer. from ctypes import string_at from sys import getsizeof a = 0x7fff print(string_at(id(a),getsizeof(a)).hex()) Output: 0200000000000000d00fbeaafe7f00000100000000000000ff7f0000 Note that this works with the CPython implementation because id() happens to return the virtual memory address of a Python object, but this … Read more
You can cast with the cast function 🙂 >>> import ctypes >>> x = (ctypes.c_ulong*5)() >>> x <__main__.c_ulong_Array_5 object at 0x00C2DB20> >>> ctypes.cast(x, ctypes.POINTER(ctypes.c_ulong)) <__main__.LP_c_ulong object at 0x0119FD00> >>>