A detailed description of the use of Python C APs (i)

Source: Internet
Author: User
Tags python list

Brief introduction

Describes the initialization and exit of Python virtual machines, the creation of objects for Python basic data types, and the conversion of data types between C and Python.

Initialization and exit of Python virtual machines

The initialization of a Python virtual machine requires a call Py_Initialize() to implement.

Py_IsInitialized()Used to determine if the Python virtual machine initialization was successful, true is successful, and false is a failure.

The virtual machine must be initialized before calling Python in C + +.

Called when exiting the virtual machine Py_Finalize() .

Exit the Python virtual machine when the process exits.

Instance:

#include <stdio.h>#include <Python.h>using namespace std;int main() {    // 初始化Python虚拟机    Py_Initialize();    // 判断Python虚拟机是否成功    if (Py_IsInitialized() == 0){        printf("fal to initialize Python\n");        return -1;    }    printf("server start\n");    // 退出Python虚拟机    Py_Finalize();    return 0;}

Compiling methods and Parameters:

下面是Python2的编译方式,Python3的话,只需要将Python的库路径改成Python3的即可g++ -I/usr/include/python2.7 -c main.cppg++ -o main main.o -L/usr/local/lib -lpython2.7 -lrt -lpthread -lutil -ldl
Pyobject

All of the object types of Python are extensions of this type. This is a type that contains the information that Python needs to treat a pointer to an object as an object. In a normal release version, it contains only the reference count of the object and a pointer to the corresponding type object. Nothing is actually declared as Pyobject, but each pointer to a Python object can be converted to Pyobject *. You must use macros PY_REFCNT and Py_type to access members.

Macro description, not including all

Py_TYPE:  获取Python对象的数据类型Py_REFCNT: Python的引用计数器Py_SIZE:  获取Python数据大小还有很多...
Py_buildvalue

You can use it to convert all of the basic data types of C to data types that Python can access.

Description of the identifier:

S (str or none) [char *] uses ' utf-8 ' encoding to convert a null-terminated C string to a Python str object. If the C string pointer is null, none is represented. s# (str or none) [Char *,int] uses the ' utf-8 ' encoding to convert the C string and its length to a Python str object. If the C string pointer is null, the length is ignored to return none. Y (bytes) [char *] This converts the C string to a Python byte object. If the C string pointer is null, none is returned. y# (bytes) [Char *,int] This converts the C string and its length to a Python object. If the C string pointer is null, none is returned. Z (str or none) [char *] is the same as S. z# (str or none) [Char *,int] is the same as s#. U (str) [Py_unicode *] Converts a null-terminated buffer of Unicode (UCS-2 or UCS-4) data to a Python UNICODE object. If the Unicode buffer pointer is NULL, none is returned. u# (str) [Py_unicode *,int] Converts the Unicode (UCS-2 or UCS-4) data buffers and their lengths to Python Unicode objects. If the Unicode buffer pointer is null, the length is ignored and none is returned. U (str or none) [char *] is the same as S. u# (str or none) [Char *,int] is the same as s#. I (int) [INT] converts a normal c int to a Python integer object. b (int) [Char] converts a pure C char to a Python integer object. h (int) [short int] Converts a normal C short int to a Python integer object. L (int) [long int] Converts a c long int to a Python integer object. B (int) [unsigned char] converts c unsigned char to a Python integer object. H (int) [unsigned short int] Converts the c unsigned short int to a Python integer object. I (int) [unsigned int] converts c unsigned int to a Python integer object. K (int) [unsigned long] converts a C unsigned long to a Python integer object. L (int) [Long long] lon C longG is converted to a Python integer object. K (int) [unsigned long long] converts the C unsigned long long to a Python integer object. n (int) [py_ssize_t] converts C py_ssize_t to a python integer. C (bytes of length 1) [Char] converts the C int representing the bytes to a Python byte object of length 1. C (str of length 1) [int] converts the C int representing the character to a Python str object of length 1. D (float) [double] converts a C double to a python floating-point number. f (float) [float] converts C float to Python floating-point number. D (complex) [Py_complex *] Converts the C Py_complex structure to the Python plural. O (object) [Pyobject *] does not change the delivery of the Python object (except the reference count, which increases by 1). If the incoming object is a null pointer, it is assumed that this is because the call that produced the argument found an error and set an exception. Therefore, Py_buildvalue () returns null but does not throw an exception. If no exception has been thrown, set systemerror. S (object) [Pyobject *] is identical to O n ((object) [Pyobject *] and O, but does not increase the reference count of the object. It is useful to create an object by calling the object constructor in the argument list. O& (object) [converter, anything] converts any content to a Python object through a converter function. The function is called anything (should be compatible with void *) as its argument, and the "new" Python object should be returned, or null if an error occurs. (items) (tuple) [Matching-items] Converts a series of c values to a Python tuple with the same number of items. [Items] (list) [Matching-items] Converts a series of c values to a Python list with the same number of items. {Items} (dict) [Matching-items] Converts a series of c values to a Python dictionary. Each pair of consecutive C values is added to the dictionary as keys and values, respectively. If there is an error in the format string, set the systemerror exception and return null.

Create a Python object of the integer type

Use to Py_BuildValue create an integer object.

void int_object(){    // 第一种方式    PyObject *py_ival = Py_BuildValue("i", -5987);   // Python有符号整型    PyObject *py_ival2 = PyLong_FromLong(-8979);    int ival = PyLong_AsLong(py_ival);   // 把Python有字符整型转换成C的有字符整型    int ival2 = PyLong_AsLong(py_ival2);   // 把Python有字符整型转换成C的有字符整型    printf("ival = %d, ival2 = %d\n", ival, ival2);    // 第二种方式    PyObject *py_uval = Py_BuildValue("I", 465486);   // Python无符号整型    PyObject *py_uval2 = PyLong_FromUnsignedLong(1654864);    unsigned int uval = PyLong_AsUnsignedLong(py_uval);        // 把Python无字符整型转换成C的无字符整型    unsigned int uval2 = PyLong_AsUnsignedLong(py_uval2);        // 把Python无字符整型转换成C的无字符整型    printf("uval = %u, uval2 = %u\n", uval, uval2);}

To create a long-integer python object

void long_object(){    // 第一种方式    PyObject *py_lval = Py_BuildValue("L", 45648946484984);   // Python 长整型    long long c_lval = PyLong_AsLongLong(py_lval);   // 转换成C的长整型    printf("clval = %lld\n", c_lval);    // 第二种方式    PyObject *py_lval2 = PyLong_FromLongLong(234234623454525);   // PyLong_FromLongLong 使用方法定义一个Python长整型    long long c_lval2 = PyLong_AsLongLong(py_lval2);   // 转换成C的长整型    printf("clval2 = %lld\n", c_lval2);}

Create a Python object of floating-point type

void double_object(){    // 第一种方式    float fval = 632.045;    PyObject *py_fval = Py_BuildValue("d", fval);   // Python 浮点类型    float c_fval = PyFloat_AsDouble(py_fval);    // C的浮点类型    printf("fval = %f\n", c_fval);    // 第二种方式    double  dval = 48941546.578;    PyObject *py_dval = PyFloat_FromDouble(dval);   // Python 浮点类型    double c_dval = PyFloat_AsDouble(py_dval);   // C的浮点类型    printf("c_dval = %lf\n", c_dval);}

Creating a Boolean type Object

void boolean_object(){    // 第一种方式    bool bval = true;   // false 反之    PyObject *py_bval = Py_BuildValue("b", bval);   // Python 布尔类型    int c_bval = PyInt_AsLong(py_bval);    printf("c_bval = %d\n", c_bval);    // 第二种方式    bool bval2 = false;    PyObject *py_bval2 = PyBool_FromLong(bval2);   // Python 布尔类型    int c_bval2 = PyInt_AsLong(py_bval2);    printf("c_bval2 = %d\n", c_bval2);}

Create a Python string object

void string_object(){    // 第一种方式    const char *pstr = "this is a test";    PyObject *py_str = Py_BuildValue("s", pstr);   // Python 字符串对象    char *c_pstr = PyString_AsString(py_str);   // 转成C的字符指针    printf("c_pstr = %s\n", c_pstr);    // 第二种方式    const char *pstr2 = "this is a test1";    PyObject *py_str2 = PyString_FromString(pstr2);   // Python 字符串对象    char *c_pstr2 = PyString_AsString(py_str2);   // 转成C的字符指针    printf("c_pstr2 = %s\n", c_pstr2);    // 创建一个二进制的字符串对象    // 第一种方式    const int mem_len = 1024;    char *mem = new char[mem_len];    PyObject *py_mem = Py_BuildValue("s#", mem, mem_len);  // 1. 数据的类型 2. 指向数据的指针 3. 数据的长度    int c_data_len = PyString_Size(py_mem);    printf("c_data_len = %d\n", c_data_len);    // 第二种方式    PyObject *py_mem2 = PyString_FromStringAndSize(mem, mem_len);    int c_data_len2 = PyString_Size(py_mem2);    printf("c_data_len2 = %d\n", c_data_len2);}

Creating a Unicode string Object

void unicode_object(){    const char *p_ustr = "兰玉磊";    PyObject *py_unicode = PyUnicode_FromString(p_ustr);  // 把C的字符串转成Python的unicode    // 把unicode转成C的字符串    PyObject *py_utf8 = PyUnicode_AsUTF8String(py_unicode);   // 把unicode转成utf-8    const char *c_string = PyString_AsString(py_utf8);   // 把utf-8转成c的字符串    printf("c_utf8 = %s\n", c_string);    // 格式化unicode字符串    // 创建一个unicode字符串    PyObject *py_unicode_fmt = PyUnicode_FromFormat("%s%d%s", "我今年", 18, "岁");    // 把unicode转C字符串    PyObject *py_utf8_fmt = PyUnicode_AsUTF8String(py_unicode_fmt);    const char *utf8_fmt = PyString_AsString(py_utf8_fmt);    printf("utf8_fmt = %s\n", utf8_fmt);}

Using Py_none

Py_Noneis a global variable

PyObject* none_object(){    Py_RETURN_NONE;   // 不需要自己return}

Main function

#include <stdio.h>#include <string.h>#include <stdlib.h>#include <Python.h>int main() {    // 初始化Python虚拟机    Py_Initialize();    // 判断Python虚拟机是否成功    if (Py_IsInitialized() == 0){        printf("fal to initialize Python\n");        return -1;    }    printf("server start\n");    int_object();    long_object();    double_object();    boolean_object();    string_object();    unicode_object();    PyObject *py_ret = none_object();    if (py_ret == Py_None){        printf("is none object\n");    }else{        printf("is not none object\n");    }    // 退出Python虚拟机    Py_Finalize();    return 0;}

A detailed description of the use of Python C APs (i)

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