What is the "correct" way to pass a boolean to a Python C extension?

What is the "correct" way to pass a boolean to a Python C extension?

In Python C extensions, you can pass a boolean value to a C function in different ways, depending on how you want to represent and use the boolean value within the C code. Here are some common approaches:

  1. Using PyBool_Check and PyBool_FromLong:

    You can use Python's PyBool_Check to check if the passed argument is a boolean, and PyBool_FromLong to convert an integer (0 or 1) into a Python boolean object. This is useful when you want to receive and return boolean values as Python True and False.

    #include <Python.h> static PyObject *my_function(PyObject *self, PyObject *args) { int bool_arg; if (!PyArg_ParseTuple(args, "i", &bool_arg)) { return NULL; } if (!PyBool_Check(bool_arg)) { PyErr_SetString(PyExc_TypeError, "Argument must be a boolean"); return NULL; } // Use bool_arg as a boolean if (bool_arg) { // True case } else { // False case } Py_RETURN_NONE; }

  2. Using PyObject_IsTrue:

    You can use PyObject_IsTrue to check the truthiness of any Python object, including booleans. This allows you to handle any Python object that can be evaluated as a boolean value.

    #include <Python.h> static PyObject *my_function(PyObject *self, PyObject *args) { PyObject *bool_arg; if (!PyArg_ParseTuple(args, "O", &bool_arg)) { return NULL; } int is_true = PyObject_IsTrue(bool_arg); if (is_true == -1) { return NULL; // Error occurred } if (is_true) { // True case } else { // False case } Py_RETURN_NONE; }

  3. Using Py_True and Py_False Constants:

    If you want to return boolean values from your C extension, you can use the Py_True and Py_False constants.

    #include <Python.h> static PyObject *my_function(PyObject *self, PyObject *args) { int bool_arg; if (!PyArg_ParseTuple(args, "i", &bool_arg)) { return NULL; } if (!PyBool_Check(bool_arg)) { PyErr_SetString(PyExc_TypeError, "Argument must be a boolean"); return NULL; } // Returning a boolean value if (bool_arg) { Py_RETURN_TRUE; } else { Py_RETURN_FALSE; } }

These approaches allow you to work with boolean values in C extensions while respecting Python's True and False conventions. Choose the method that best fits your use case and coding style.

Examples

  1. "How to pass a boolean from Python to a C extension?"

    • This query explores the basics of passing a boolean value from Python to a C extension.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { // 'p' is for boolean return NULL; } if (my_bool) { Py_RETURN_TRUE; } else { Py_RETURN_FALSE; } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "A sample function"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  2. "Python C extension for boolean input with default value"

    • This query explores how to use a default value when a boolean is not passed from Python to a C extension.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool = 0; // Default to False if (!PyArg_ParseTuple(args, "|p", &my_bool)) { // '|' means optional return NULL; } return Py_BuildValue("i", my_bool); // Return the integer representation } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "A sample function with default"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  3. "Using Py_BuildValue to return booleans from Python C extension"

    • This query explains how to return a boolean value from a C extension using Py_BuildValue.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { return NULL; } return Py_BuildValue("p", my_bool); // Return as a boolean } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Return boolean"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  4. "Handling boolean arguments in a Python C extension with error handling"

    • This query explores error handling when parsing boolean arguments in a Python C extension.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { PyErr_SetString(PyExc_TypeError, "Expected a boolean"); return NULL; } return my_bool ? Py_True : Py_False; } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Return True or False"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  5. "Python C extension: checking and returning boolean values"

    • This query demonstrates checking a boolean argument and returning appropriate values.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { return NULL; } if (my_bool) { return Py_BuildValue("s", "The argument was True"); } else { return Py_BuildValue("s", "The argument was False"); } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Check and return boolean status"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  6. "Python C extension with multiple arguments including booleans"

    • This query demonstrates parsing multiple arguments, including booleans, in a C extension.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int a; int b; int my_bool; if (!PyArg_ParseTuple(args, "iip", &a, &b, &my_bool)) { return NULL; } if (my_bool) { return Py_BuildValue("i", a + b); // Return the sum if True } else { return Py_BuildValue("i", a * b); // Return the product if False } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Process integers and boolean"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  7. "Combining boolean parsing with other data types in Python C extension"

    • This query explains how to parse boolean values along with other data types like strings and integers.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int age; char* name; int my_bool; if (!PyArg_ParseTuple(args, "sip", &age, &name, &my_bool)) { return NULL; } if (my_bool) { return Py_BuildValue("s", f"{name} is {age} and boolean was True"); } else { return Py_BuildValue("s", f"{name} is {age} and boolean was False"); } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Parse name, age, and boolean"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  8. "Returning different types based on boolean input in Python C extension"

    • This query demonstrates how to return different data types based on a boolean input.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { return NULL; } if (my_bool) { return Py_BuildValue("i", 42); // If True, return integer } else { return Py_BuildValue("s", "Hello, World"); // If False, return string } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Return different types based on boolean"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  9. "Handling error cases when parsing booleans in Python C extension"

    • This query explores how to manage error handling when parsing boolean values in a C extension.
    • #include <Python.h> static PyObject* my_function(PyObject* self, PyObject* args) { int my_bool; if (!PyArg_ParseTuple(args, "p", &my_bool)) { PyErr_SetString(PyExc_TypeError, "Expected a boolean value"); return NULL; } if (my_bool) { return Py_BuildValue("s", "You passed True"); } else { return Py_BuildValue("s", "You passed False"); } } static PyMethodDef MyMethods[] = { {"my_function", my_function, METH_VARARGS, "Handle boolean with error handling"}, {NULL, NULL, 0, NULL} }; static struct PyModuleDef mymodule = { PyModuleDef_HEAD_INIT, "mymodule", NULL, -1, MyMethods }; PyMODINIT_FUNC PyInit_mymodule(void) { return PyModule_Create(&mymodule); }

  10. "Python C extension: converting booleans to integers for output"

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