fatal error: Python.h: No such file or directory when compiling pybind11 example

Question

I am starting out with pybind11, trying to compile the first example. I am using Xubuntu 20.04. My system python is 3.8, but I have install pybind11 only for python 3.10, which is the version that executes when I type python at the command prompt. When I run the compilation command given in the pybind11 docs:

c++ -O3 -Wall -shared -std=c++11 -fPIC $(python3.10 -m pybind11 --includes) example.cpp -o example$(python3.10-config --extension-suffix)

I get the error message:

     fatal error: Python.h: No such file or directory
  213 | #include <Python.h>

I followed the advice give in the accepted answer to fatal error: Python.h: No such file or directory, and ran

sudo apt install python3.10-dev

but this had no effect, even though Python.h now exists in /usr/include/python3.10. I should perhaps mention that I am not using a virtual environment at this point.

EDIT

python3.10-config --cflags
-I/usr/include/python3.10 -I/usr/include/python3.10  -Wno-unused-result -Wsign-compare -g   -fstack-protector-strong -Wformat -Werror=format-security  -DNDEBUG -g -fwrapv -O2 -Wall

EDIT

I changed the command as suggested by 9769953:

Pybind11Test$ c++ -O3 -Wall -shared -std=c++11 -fPIC $(python3.10 -m pybind11 python3.10-config --includes) example.cpp -o example$(python3.10-config --extension-suffix)
usage: __main__.py [-h] [--includes] [--cmakedir]
__main__.py: error: unrecognized arguments: python3.10-config
example.cpp:1:10: fatal error: pybind11/pybind11.h: No such file or directory
    1 | #include <pybind11/pybind11.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Adding python3.10-config gave me an unrecognized argumnents error, but the compilation failed at a different place. #include <pybind11/pybind11.h> is the first line of example.cpp.

The file exists at

/home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/pybind11.h

EDIT

Latest attempt

Pybind11Test$ c++ -O3 -Wall -shared -std=c++11 -fPIC $(python3.10 -m pybind11 --includes) example.cpp -o example.out
In file included from /home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/detail/../cast.h:13,
                 from /home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/detail/../attr.h:13,
                 from /home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/detail/class.h:12,
                 from /home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/pybind11.h:13,
                 from example.cpp:1:
/home/saul/.local/lib/python3.10/site-packages/pybind11/include/pybind11/detail/../detail/common.h:213:10: fatal error: Python.h: No such file or directory
  213 | #include <Python.h>
      |          ^~~~~~~~~~
compilation terminated.

@9769953 It's the one from python3.8. I don't seem to have a `python3-config` file for 3.10 — saulspatz, Jun 04 '22 at 18:53
@9769953 I didn't realize that. I assumed that apt would update the database. — saulspatz, Jun 04 '22 at 18:54
@9769953 Give me I a minute and I will edit the body of the question to include all this information. I appreciate your help — saulspatz, Jun 04 '22 at 19:02
@9769953 Making the changes to the compilation command that you suggested had no effect — saulspatz, Jun 04 '22 at 19:13
@9769953 Please see my edits to the question body. I wonder if `pybind11` is installed wrong somehow. — saulspatz, Jun 04 '22 at 19:29
Now i get `c++: error: .cpython-310-x86_64-linux-gnu.so: No such file or directory` — saulspatz, Jun 04 '22 at 19:54
No extra space, but I think it's an installation problem. When I go to /home/saul/.local/lib/python3.10/site-packages/pybind11/share there are no binary files, but there is a cmake directory. I don't see that the instructions at https://pybind11.readthedocs.io/en/stable/installing.html say anything about cmake, though. — saulspatz, Jun 04 '22 at 20:03
Changing the executable to example.out gets me back to `Python.h` not found. Please see my latest edit. — saulspatz, Jun 04 '22 at 20:16
That worked! Thank you. If you want to an answer, I'll be happy to accept it. — saulspatz, Jun 04 '22 at 20:38
I introduced an extraneous `--includes` in the extension-suffix part. The root cause was the missing `$(python3.10-config --includes)` Once again, thanks so much — saulspatz, Jun 04 '22 at 20:50

fatal error: Python.h: No such file or directory when compiling pybind11 example

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