DLL & Python

Recently I was interested in the topic of using DLLs from Python. In addition, it was interesting to understand their structure, in case you have to change the source of the libraries. After studying various resources and examples on this topic, it became clear that the use of dynamic libraries can greatly expand the capabilities of Python. My own goals were achieved, and so that the experience was not forgotten, I decided to summarize in the form of an article - to structure my knowledge and useful sources, and at the same time to better understand this topic.

Under the cut you will find an article with various examples, sources and explanations for them.

Content

DLL structure
DLL & Python
- DLL connection
- Data Types in C and Python
- Arguments function and return values
- Own DLL and its use
Useful links:

, .

DLL

DLL — Dynamic Link Library — () Windows. , . .EXE — , DLL .

, , Microsoft: DLL?.

, , , .

DLL , -. . DllMain , DLL . .

1 — template, Code Blocks DLL.

1 , Code Blocks, DLL. :

#define DLL_EXPORT __declspec(dllexport) //   , 
                                         //                                                      // 
void DLL_EXPORT SomeFunction(const LPCSTR sometext); //    ,

extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) //

DllMain. (fdwReason):

DLL_PROCESS_ATTACH – DLL. DLL . DllMain , - .
DLL_PROCESS_DETACH – DLL . DllMain .
DLL_THREAD_ATTACH – , DLL, . DLL - ? , .
DLL_THREAD_DETACH – , , DLL. "" ( ), .

, DLL , , .

DllMain , fdwReason , :

lpvReserved DLL:
- 0 — .
- 1 — .
hinstDLL DLL. EXE- DLL-, , .

: DLL.

1 SomeFunction, . , , __declspec(dllexport). , :

#define DLL_EXPORT __declspec(dllexport) 
void DLL_EXPORT SomeFunction(const LPCSTR sometext);

, , .

DLL & Python

, , DLL, , , , Code Blocks DLL.

DLL

Python , ctypes. ctypes , .

DLL, Python. :

cdll — , DLL . cdecl.
windll — stdcall. cdll.
oledll — stdcall , Windows HRESULT. WindowsError.

Windows DLL , — printf(). msvcrt.dll C:\WINDOWS\System32.

Python:

from ctypes import *

lib = cdll.msvcrt   #   msvcrt.dll
lib.printf(b"From dll with love!\n") #     printf

var_a = 31
lib.printf(b"Print int_a = %d\n", var_a) #   int 
                                # printf("Print int_a = %d\n", var_a); //

From dll with love!
Print int_a = 31

windll oledll, , .

, dll. ctypes LoadLibrary. CDLL, cdll.LoadLibrary. , msvcrt.dll.

Python:

from ctypes import *

lib = cdll.LoadLibrary(r"C:\Windows\System32\msvcrt.dll")   
lib.printf(b"From dll with love!\n")    #     printf

lib_2 = CDLL(r"C:\Windows\System32\msvcrt.dll") #   msvcrt.dll

var_a = 31
lib_2.printf(b"Print int_a = %d\n", var_a)  #   int

, DLL, Python ""… . getattr(lib, attr_name). : , .

Python:

from ctypes import *

lib = cdll.LoadLibrary(r"C:\Windows\System32\msvcrt.dll")   

var_c = 51
print_from_C = getattr(lib, "printf")  # ,     "??2@YAPAXI@Z"
print_from_C(b"Print int_c = %d\n", var_c)

Print int_c = 51

, . , DLL . , , . , , .

Python

ctypes . .

types type	C type	Python type
`c_bool`	`_Bool`	bool (1)
`c_char`	`char`	1-character string
`c_wchar`	`wchar_t`	1-character unicode string
`c_byte`	`char`	int/long
`c_ubyte`	`unsigned char`	int/long
`c_short`	`short`	int/long
`c_ushort`	`unsigned short`	int/long
`c_int`	`int`	int/long
`c_uint`	`unsigned int`	int/long
`c_long`	`long`	int/long
`c_ulong`	`unsigned long`	int/long
`c_longlong`	`__int64` or `long long`	int/long
`c_ulonglong`	`unsigned __int64` or `unsigned long long`	int/long
`c_float`	`float`	float
`c_double`	`double`	float
`c_longdouble`	`long double`	float
`c_char_p`	`char *` (NUL terminated)	string or `None`
`c_wchar_p`	`wchar_t *` (NUL terminated)	unicode or `None`
`c_void_p`	`void *`	int/long or `None`

1 — Python C, ctypes.

, — , ? , , printf() :

from ctypes import *

lib = CDLL(r"C:\Windows\System32\msvcrt.dll")
printf = lib.printf #   printf()

int_var = c_int(17) #   int  C
printf(b"int_var = %d\n", int_var)

str_ = b"Hello, World\n" #   Python
str_pt = c_char_p(str_)  #   
printf(str_pt)           

print(str_pt)            
print(str_pt.value) # str_pt -   ,       value

int_var = 17
Hello, World
c_char_p(2814054827168)
b'Hello, World\n'

, ( , ) value, .

, int. restype. , argtypes.

, strcat . .

char *strcat (char *destination, const char *append); // C    ()

Python:

from ctypes import *

libc = CDLL(r"C:\Windows\System32\msvcrt.dll")

strcat = libc.strcat        #    strcat
strcat.restype = c_char_p   # ,                                       # 
strcat.argtypes = [c_char_p, c_char_p] #    

str_1 = b"Hello,"
str_2 = b" Habr!"
str_pt = strcat(str_1, str_2) #   

print(str_pt)

b'Hello, Habr!'

DLL. DLL ctypes , .

DLL

1

DLL , , DLL , — DLL Python. Python x64, , DLL , DLL Python. , x64 Python x64, x32. , .

DLL, , , DllMain. , .

DLL :

// a sample exported function
void __declspec(dllexport) SomeFunction(const LPCSTR sometext)
{
    MessageBoxA(0, sometext, "DLL Message", MB_OK | MB_ICONINFORMATION);
}

extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    switch (fdwReason)
    {
        case DLL_PROCESS_ATTACH:
            printf("Load DLL in Python\n");

            printf("HINSTANCE = %p\n",hinstDLL); //    DLL

            if (lpvReserved)                     //   
              printf("DLL loaded with implicit layout\n"); 
            else
              printf("DLL loaded with explicit layout\n");          
            return 1;                            //  

        case DLL_PROCESS_DETACH:
            printf("DETACH DLL\n");
            break;

        case DLL_THREAD_ATTACH:
            break;

        case DLL_THREAD_DETACH:
            break;
    }
    return TRUE; // succesful
}

Python:

from ctypes import *

lib_dll = cdll.LoadLibrary("DLL_example.dll")   #   DLL
str_ = b'Hello, Habr!'
p_str = c_char_p(str_)                          #     str_
lib_dll.SomeFunction(p_str)                     #  SomeFunction  DLL

SomeFunction . .

2 — Code Blocks.

DLL_PROCESS_ATTACH, , Python :

lib_dll = cdll.LoadLibrary("DLL_example.dll")   #

3 — DLL.

2

DLL Python, , . , Python. main.c, man.h main.py.

DLL :

main.h

#ifndef __MAIN_H__
#define __MAIN_H__

#include <windows.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>

#define DLL_EXPORT __declspec(dllexport) //   , 
                                         //                                                      // 
#ifdef __cplusplus
extern "C"
{
#endif

struct Passport{
    char*  name;
    char*  surname;
    int var;
};

void DLL_EXPORT SetName(char* new_name);
void DLL_EXPORT SetSurname(char* new_surname);
void DLL_EXPORT SetPassport(Passport* new_passport);
void DLL_EXPORT GetPassport(void);

#ifdef __cplusplus
}
#endif
#endif // __MAIN_H__

main.h Passport : . , , .

DLL :

main.c

#include "main.h"

#define SIZE_BUF 20

struct Passport passport; //   passport  Passport

//   
void DLL_EXPORT SetName(char* new_name)
{
    printf("SetName\n");
    strcpy(passport.name, new_name);
}

//   
void DLL_EXPORT SetSurname(char* new_surname)
{
    printf("SetSurname\n");
    strcpy(passport.surname, new_surname);
}

//    .
//      
void DLL_EXPORT SetPassport(Passport* new_passport)
{
    printf("SetPassport\n");
    strcpy(passport.name, new_passport->name);
    strcpy(passport.surname, new_passport->surname);
    passport.var = new_passport->var;
}

//     
void DLL_EXPORT GetPassport(void)
{
    printf("GetPassport: %s | %s | %d\n", passport.name, passport.surname, passport.var);
}

extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    switch (fdwReason)
    {
        case DLL_PROCESS_ATTACH:
            printf("Load DLL in Python\n");

            passport.name = (char*)malloc(SIZE_BUF * sizeof(char)); //  
            passport.surname = (char*)malloc(SIZE_BUF * sizeof(char)); //  

            passport.var = 17; //   
            SetName("Default"); //    
            SetSurname("Passport"); //    
            return 1;

        case DLL_PROCESS_DETACH:
            free (passport.name); //  
            free (passport.surname); //  
            printf("DETACH DLL\n");
            break;

        case DLL_THREAD_ATTACH:
            break;

        case DLL_THREAD_DETACH:
            break;
    }
    return TRUE; // succesful
}

DLL_PROCESS_ATTACH . DllMain :

GetPassport — passport .
*SetName(char new_name)** — name passport.
*SetSurname(char new_surname)** — surname passport.
*SetPassport(Passport new_passport)** — passport. .

Python.

Python

from ctypes import *

class Passport(Structure):              # ,    Passport 
    _fields_ = [("name", c_char_p),    #   main.h
                ("surname", c_char_p),
                ("var", c_int)]

lib_dll = cdll.LoadLibrary("DLL_example.dll")   #   DLL
lib_dll.SetPassport.argtypes  = [POINTER(Passport)] # ,   

lib_dll.GetPassport()          #    

lib_dll.SetName(c_char_p(b"Yury"))
lib_dll.SetSurname(c_char_p(b"Orlov"))

lib_dll.GetPassport()         #    

name = str.encode(("Vasiliy"))  #       
surname = c_char_p((b'Pupkin')) #       

passport = Passport(name, surname, 34) #    Passport

lib_dll.SetPassport(pointer(passport)) #      DLL

lib_dll.GetPassport()         #

, , DLL Python DLL.

Load DLL in Python
SetName
SetSurname
GetPassport: Default | Passport | 17
SetName
SetSurname
GetPassport: Yury | Orlov | 17
SetPassport
GetPassport: Vasiliy | Pupkin | 34
DETACH DLL

P.S: , DLL Python. . - — , — . , !

:

ctypes —
DLL? — dll.
[C/C++ Python (ctypes)](C/C++ Python (ctypes)) — .
python DLL
DLL
Github dll "Hello-world" — .
TCHAR, WCHAR, LPSTR, LPWSTR,LPCTSTR — .
Dynamic Gourmet Libraries - an article with a lot of interesting nuances.

DLL & Python

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