Specifying Python function signature in C/API

Question

When defining a function in pure Python, its signature is visible when calling help. For example:

>>> def hello(name):
... """Greet somebody."""
... print "Hello " + name
...
>>> help(hello)
Help on function hello in module __main__:
hello(name)
 Greet somebody.
>>>

When defining a Python function in C/API, though, its signature lacks basic information:

static PyObject*
mod_hello(PyObject* self, PyObject* args)
{
 const char* name;
 if (!PyArg_ParseTuple(args, "s", &name))
 return NULL;
 printf("Hello %s\n", name);
 Py_RETURN_NONE;
}
static PyMethodDef HelloMethods[] =
{
 {"hello", mod_hello, METH_VARARGS, "Greet somebody."},
 {NULL, NULL, 0, NULL}
};

This yields:

>>> help(hello)
Help on built-in function hello in module hello:
hello(...)
 Greet somebody.

Any ideas how, in C/API, to change the signature from hello(...) to hello(name)?

• boardrider: I assume you read stackoverflow.com/questions/1104823/… ?

Answer 1

You can include the signature by prepending it to the function docstring in a way that inspect can extract them (at least it works for Python 3.4+):

static PyMethodDef HelloMethods[] =
{
 {"hello", mod_hello, METH_VARARGS, "hello(name, /)\n--\n\nGreet somebody."},
 {NULL, NULL, 0, NULL}
};

Note I've posted a more complete answer here that explain the rules and mechanics in some more depth.