__call__和__new__
时间: 2023-07-03 07:24:46 浏览: 41
`__call__`和`__new__`都是Python中的特殊方法,用于创建和调用对象。
`__new__`方法在对象创建之前被调用,通常用于自定义对象的构造过程。它返回一个新的对象实例,该实例将被传递给`__init__`方法进行初始化。`__new__`方法通常用于创建不可变对象或单例模式。
`__call__`方法使得一个对象可以像函数一样进行调用。当一个对象被调用时,Python会查找该对象的`__call__`方法并执行它。`__call__`方法通常用于实现可调用的类,如装饰器或上下文管理器。
需要注意的是,`__new__`方法是一个类方法,接受的第一个参数是类本身,而`__call__`方法则是一个实例方法,接受的第一个参数是实例本身。
相关问题
PyObject_CallFunction
PyObject_CallFunction是一个Python C API函数,用于调用一个Python函数并传递参数。它的参数包括一个PyObject对象(表示函数),一个字符串(表示参数类型),以及一个或多个PyObject对象(表示函数的参数)。\[1\]
例如,如果我们有一个名为"my_function"的Python函数,它接受一个整数参数,我们可以使用PyObject_CallFunction来调用它:
```
PyObject_CallFunction(my_function, "i", 42);
```
这将调用my_function,并将整数值42作为参数传递给它。
另外,PyObject_CallMethod是一个类似的函数,用于调用一个Python类的方法。它的参数包括一个PyObject对象(表示类),一个字符串(表示方法名),一个字符串(表示参数类型),以及一个或多个PyObject对象(表示方法的参数)。\[2\]
例如,如果我们有一个名为"my_method"的类方法,它接受一个整数参数,并且我们有一个类实例pInstance,我们可以使用PyObject_CallMethod来调用它:
```
PyObject_CallMethod(pClass, "my_method", "i", pInstance, 42);
```
这将调用pClass的my_method,并将整数值42以及pInstance作为参数传递给它。
最后,创建一个元组可以使用Python C API中的PyTuple_New和PyTuple_SetItem函数。首先,使用PyTuple_New创建一个空的元组对象,然后使用PyTuple_SetItem将元素添加到元组中。\[3\]
例如,以下代码创建一个包含三个整数的元组:
```
PyObject *pArgs = PyTuple_New(3);
PyTuple_SetItem(pArgs, 0, Py_BuildValue("i", 1));
PyTuple_SetItem(pArgs, 1, Py_BuildValue("i", 2));
PyTuple_SetItem(pArgs, 2, Py_BuildValue("i", 3));
```
这将创建一个元组(1, 2, 3)。
总结起来,PyObject_CallFunction和PyObject_CallMethod是用于调用Python函数和类方法的函数,而PyTuple_New和PyTuple_SetItem是用于创建元组的函数。
#### 引用[.reference_title]
- *1* *2* *3* [C++中嵌入python程序——参数传递](https://blog.csdn.net/yiyouxian/article/details/51995029)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^koosearch_v1,239^v3^insert_chatgpt"}} ] [.reference_item]
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subprocess.check_call
subprocess.check_call is a Python method that is used to execute a command or a program in a new process. It is a blocking call, which means that the calling process will wait for the command to complete before continuing execution. If the command returns a non-zero exit status, a CalledProcessError will be raised. This method is commonly used for running shell commands in Python scripts.
Syntax:
```
subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, encoding=None, errors=None)
```
Parameters:
- args: A string or a sequence containing the command to be executed and its arguments.
- stdin: A file-like object representing the standard input of the command. If None, the standard input is redirected to /dev/null.
- stdout: A file-like object representing the standard output of the command. If None, the standard output is redirected to /dev/null.
- stderr: A file-like object representing the standard error of the command. If None, the standard error is redirected to stdout.
- shell: A boolean value indicating whether the command should be executed in a shell or not. If True, the command is executed in a shell. If False, the command is executed directly.
- cwd: The working directory in which the command should be executed.
- timeout: The maximum amount of time in seconds that the command is allowed to run. If the command takes longer than the specified timeout, a TimeoutExpired error is raised.
- encoding: The character encoding to be used for the standard input, output, and error streams.
- errors: The error handling strategy to be used for the standard input, output, and error streams.
Return Value:
- This method returns None if the command is executed successfully. If the command returns a non-zero exit status, a CalledProcessError is raised.