Python Import Error: Undefined Symbol for Custom C Module

I've been experimenting with C modules in python and I've had no problems with compilation. However, when it comes to importing the module I receive this error message:

>>> import _strrev
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: /path/to/my/module.so: undefined symbol: strrev

The contents of the file are

_strrev.c

#include <Python.h>
#include <string.h>
static PyObject* _strrev(PyObject* self, PyObject *args) {
   PyObject* name;
   if (!PyArg_ParseTuple(args, "U", &name)) {
       return NULL; 
   }
   PyObject *ret = strrev(*name); 

   return ret;
}

static struct PyMethodDef methods[] = {
    {"strrev", (PyCFunction)_strrev, METH_VARARGS},
    {NULL, NULL}
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT, 
    "_strrev",
    NULL, 
    -1, 
    methods
};

PyMODINIT_FUNC PyInit__strrev(void) {
    return PyModule_Create(&module);
}

setup.py

from distutils.core import setup, Extension

setup(
        name='strrev_lib',
        version='1',
        ext_modules=[Extension('_strrev', ['_strrev.c'])],
        )

When running nm -D on this object file, I get this output

$ nm -D _strrev.cpython-39-x86_64-linux-gnu.so 
                 w __cxa_finalize@GLIBC_2.2.5
                 w __gmon_start__
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 U PyArg_ParseTuple
00000000000011a0 T PyInit__strrev
                 U PyModule_Create2
                 U __stack_chk_fail@GLIBC_2.4
                 U strrev

I can see that strrev is here, so I don't understand why it says that the symbol in undefined.

I've also tried using a different module and that works perfectly fine when attempting to import it.

$ python3
Python 3.9.2 (default, Feb 28 2021, 17:03:44) 
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import _hello
>>> _hello.hello("Jared")
'hello Jared'

The contents of the files are:
_hello.c

#include <Python.h>

static PyObject* _hello(PyObject* self, PyObject *args) {
   PyObject* name;
   if (!PyArg_ParseTuple(args, "U", &name)) {
       return NULL; 
   }
   PyObject *ret = PyUnicode_FromFormat("hello %U", name);

   return ret;
}

static struct PyMethodDef methods[] = {
    {"hello", (PyCFunction)_hello, METH_VARARGS},
    {NULL, NULL}
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT, 
    "_hello",
    NULL, 
    -1, 
    methods
};

PyMODINIT_FUNC PyInit__hello(void) {
    return PyModule_Create(&module);
}

setup.py

from setuptools import setup
from setuptools import Extension

setup(
        name='hello-lib',
        version='1',
        ext_modules=[Extension('_hello', ['_hello.c'])],
        )

Can anyone give me pointers as to what I'm doing wrong? Is it something with the compilation or with the code that I've written? Any help would be appreciated!

> I can see that strrev is here, so I don't understand why it says that the symbol in undefined.

Au contraire: you can see that strrev is not there -- U in nm output means undefined.

The strrev appears to be a Windows thing, and you are not on Windows. There is no such symbol in GLIBC:

$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep strrev
$

To fix this, you would need to implement strrev() yourself.