Introduction to two common functions in lower-level Python embedding

This article mainly introduces the introduction of two types of functions commonly used in Python embedding at a lower level, as well as the actual application steps of the two types of functions and the specific introduction of the relevant code, the following is a detailed description of the article. I hope you will get what you want after browsing.

In the example in the previous section, only simple functions are used to embed Python into the C language. However, if you need to use a Python script to PASS Parameters in the C program or obtain the return value of the Python script, you need to use more functions to compile the C program. Because Python has its own data type, special APIs should be used in the C program to operate the corresponding data type. Common functions are as follows.

1. Processing numbers and strings

The Python/c api provides the Py_BuildValue () function to convert numbers and strings to the corresponding data type in Python. The function prototype is as follows.

 
 

  
  
PyObject* Py_BuildValue( const char *format, ...) 
 
 

The parameter meanings are as follows.

· Format: format the string, as shown in Table 8-1.

 
 

  
  
Py_BuildValue() 
 
 

The remaining parameters in the function are integer, floating point, or string values in the C language to be converted. The returned value is a pointer of the PyObject type. In C, all Python types are declared as PyObject.

2. List operations

Python/c api provides the PyList_New () function to create a new Python list. The Return Value of the PyList_New () function is the list created. The function prototype is as follows.

 
 

  
  
PyObject* PyList_New( Py_ssize_t len) 
 
 

The parameter meanings are as follows.

· Len: the length of the created list.

After the list is created, you can use the PyList_SetItem () function to add items to the list. The function prototype is as follows.

 
 

  
  
int PyList_SetItem( PyObject *list,
 Py_ssize_t index, PyObject *item) 
 
 

The parameter meanings are as follows.

· List: list of items to be added.

· Index: Location index of the added item.

· Item: the value of the added item.

You can also use the PyList_GetItem () function in Python/c api to obtain the value of an item in the list. The value returned by the PyList_GetItem () function. The function prototype is as follows.

 
 

  
  
PyObject* PyList_GetItem
( PyObject *list, Py_ssize_t index) 
 
 

The above section describes the commonly used functions embedded in lower layers of Python.