python高效能擴充套件工具-cython教程2基礎

摘要： 本章涉及的主要內容： 連結模型 Cython關鍵字 - cdef Typedef和函式指標 public關鍵字 關鍵字cpdef C/C+++呼叫Python logging C/C++用Python ConfigParser Python...

本章涉及的主要內容：

• 連結模型
• Cython關鍵字 - cdef
• Typedef和函式指標
• public關鍵字
• 關鍵字cpdef
• C/C+++呼叫Python logging
• C/C++用Python ConfigParser
• Python到C/C++的回撥
• Cython PXD
• 與構建系統整合

連結模型

C/C++中嵌入python

cython模式

cdef

cdef關鍵字告訴編譯器該語句是本地C型別或本地函式。比如：

cdef int AddFunction(int, int)

def square(int x):
return x ** 2

Struct

C的struct 可以直接在Cython中使用。比如mycode.h

#ifndef __MYCODE_H__
#define __MYCODE_H__

struct mystruct {
char * string;
int integer;
char ** string_array;
};

extern void printStruct (struct mystruct *);

#endif //__MYCODE_H__

printStruct函式的實現 mycode.c

#include <stdio.h>
#include "mycode.h"

void printStruct (struct mystruct * s)
{
printf (".string = %s\n", s->string);
printf (".integer = %i\n", s->integer);
printf (".string_array = \n");

int i;
for (i = 0; i < s->integer; ++i)
printf ("\t[%i] = %s\n", i, s->string_array [i]);
}

Python匯入呼叫：mycodepy.pyx

cdef extern from "mycode.h":
struct mystruct:
char * string
int integer
char ** string_array
void printStruct (mystruct *)

def testStruct ():
cdef mystruct s
cdef char *array [2]
s.string = "Hello World"
s.integer = 2
array [0] = "foo"
array [1] = "bar"
s.string_array = array
printStruct (&s)

巢狀結構體void myfunc (struct mystruct * x)在cython的定義：void myfunc (mystruct * x)。cython中沒有→操作符號，要使用點號。

執行

$ make
cython -3 -o mycodepy.c mycodepy.pyx
gcc -g -O2 -fpic -c mycodepy.c -o mycodepy.o `python3-config --cflags`
gcc -g -O2 -fpic -c mycode.c -o mycode.o
gcc -g -O2 -shared -o mycodepy.so mycode.o mycodepy.o
$ python
Python 3.6.5 |Anaconda, Inc.| (default, Apr 29 2018, 16:14:56) 
[GCC 7.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from mycodepy import testStruct
>>> from mycodepy import testStruct
>>> testStruct ()
.string = Hello World
.integer = 2
.string_array = 
[0] = foo
[1] = bar

Enum

c中的實現：

enum cardsuit {
CLUBS,
DIAMONDS,
HEARTS,
SPADES
};

Cython定義

cdef enum cardsuit:
CLUBS, DIAMONDS, HEARTS, SPADES

# 使用
cdef cardsuit card = CLUBS

Typedef和函式指標

c中的實現：

struct foobar {
int x;
char * y;
};

typedef struct foobar foobar_t;
typedef void (*cfptr) (int)

Cython定義

cdef struct foobar:
int x
char * y
ctypedef foobar foobar_t

# 使用
ctypedef int * int_ptr
ctypedef void (*cfptr)(int
cdef cfptr myfunctionptr = &myfunc

Typedef和函式指標

這是Cython中非常強大的關鍵字。 它允許任何帶有public修飾符的cdef宣告輸出相應的C/C++頭，其中相關宣告可從C/C++訪問。 例如，我們可以宣告：

cdef public struct CythonStruct:
size_t number_of_elements;
char ** elements;

編譯後會生成cython_input.h

struct CythonStruct {
size_t number_of_elements;
char ** elements;
};

c呼叫要求在嵌入libpython.so，並執行初始化：

#include <Python.h>

int main(int argc, char **argv) {
Py_Initialize ();
// code in here
Py_Finalize ();
return 0;
}

呼叫前需要初始化cythonfile.pyx(如果有)的

cdef public void cythonFunction ():
print "inside cython function!!!"

這樣會生成cythonfile.c和cythonfile.h。

/* Boiler plate init Python */
Py_SetProgramName (argv [0]);
Py_Initialize ();
/* Init our config module into Python memory */
initpublicTest ();
cythonFunction ();
/* cleanup python before exit... */
Py_Finalize ();

這個步驟類似python中的import cythonfile

cpdef

函式宣告def在python和cython中可呼叫，cdef在c系列可以呼叫，cpdef在兩者都可以呼叫，但是返回要知道型別，且喪失了cython的型別安全，不推薦這麼做。

long returnValue = PyInt_AsLong (test (1, 0))

例項：C/C++呼叫python logging

main.c

#include "NativeLogging.h"

int main(int argc, char **argv)
{
// we want to ensure we use a command line argument for the output log file
if (argc < 2) {
return -1;
}

// use the first argument as log file
SetupNativeLogging(argv[1]);

// log out some stuff at different levels
info("info message");
debug("debug message");
error("error message");

// close up everything including Python
CloseNativeLogging();

return 0;
}

NativeLogging.h

#ifndef __NATIVE_LOGGING_H__
#define __NATIVE_LOGGING_H__

#define printflike __attribute__ ((format (printf, 3, 4)))

extern void printflike native_logging_info(const char *, unsigned, const char *, ...);
extern void printflike native_logging_debug(const char *, unsigned, const char *, ...);
extern void printflike native_logging_error(const char *, unsigned, const char *, ...);

#define info(...)native_logging_info(__FILE__, __LINE__, __VA_ARGS__)
#define error(...) native_logging_debug(__FILE__, __LINE__, __VA_ARGS__)
#define debug(...) native_logging_error(__FILE__, __LINE__, __VA_ARGS__)

extern void SetupNativeLogging(const char * logFileName);
extern void CloseNativeLogging();

#endif // __NATIVE_LOGGING_H__

NativeLogging.c

#include <Python.h>
#include <stdio.h>
#include <stdarg.h>

#include "PythonLoggingBackend.h"
#include "NativeLogging.h"

void native_logging_info(const char * file, unsigned line, const char * fmt, ...)
{
char buffer[256];
va_list args;
va_start(args, fmt);
vsprintf(buffer, fmt, args);
va_end(args);

char buf[512];
snprintf(buf, sizeof(buf), "%s:%i -> %s", file, line, buffer);
python_info(buf);
}

void native_logging_debug(const char * file, unsigned line,const char * fmt, ...)
{
char buffer[256];
va_list args;
va_start(args, fmt);
vsprintf(buffer, fmt, args);
va_end(args);

char buf[512];
snprintf(buf, sizeof(buf), "%s-%i -> %s", file, line, buffer);
python_debug(buf);
}

void native_logging_error(const char * file, unsigned line, const char * fmt, ...)
{
char buffer[256];
va_list args;
va_start(args, fmt);
vsprintf(buffer, fmt, args);
va_end(args);

char buf[512];
snprintf(buf, sizeof(buf), "%s:%i -> %s", file, line, buffer);
python_error(buf);
}

void SetupNativeLogging(const char * logFileName)
{
/* Boiler plate init Python */
Py_Initialize();

/* Init our config module into Python memory */
initPythonLoggingBackend();

/* call directly into our cython module parseConfig */
initLoggingWithLogFile(logFileName);
}

void CloseNativeLogging()
{
/* cleanup python before exit ... */
Py_Finalize();
}

PythonLoggingBackend.pyx

import logging

cdef public void initLoggingWithLogFile(const char * logfile):
logging.basicConfig(filename = logfile,
level = logging.DEBUG,
format = '%(levelname)s %(asctime)s: %(message)s',
datefmt = '%m/%d/%Y %I:%M:%S')

cdef public void python_info(char * message):
logging.info(message)

cdef public void python_debug(char * message):
logging.debug(message)

cdef public void python_error(char * message):
logging.error(message)

Makefile

all:
cython -2 PythonLoggingBackend.pyx
gcc -g -O2 -fpic -c PythonLoggingBackend.c -o PythonLoggingBackend.o `python-config --includes`
gcc -g -O2 -fpic -c NativeLogging.c -o NativeLogging.o`python-config --includes`
gcc -g -O2 -fpic -c main.c -o main.o
gcc -g -O2 -o example main.o PythonLoggingBackend.o NativeLogging.o `python-config --libs`

clean:
rm -f example PythonLoggingBackend.c *.o PythonLoggingBackend.h *.log