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Python/C++ wrapper Using external dll with Pybind11

Python version: 3.8.1
Spyder version: 3.3.6
Qt version: 5.12.9
Wrapper: develop using PyBind11
I am wrapping a dll develop in C++ which use Qt dlls to be used with Python. I wrote the wrapper with Visual Studio 2019 using the compiler MSVC (as my dll is compiled with MSVC). After generating the solution in VS2019 I obtain a .pyd file which can be import with python.
It works good when I use python on line command:
Start cmd.exe
$python
import MyLibName
I can use the functions/classes ...
But if I try with Spyder, I get the following error:
ImportError: DLL load failed while importing PyStack: The specified module could not be found..
So here are my questions :
Is there a way to get more information about ImportError like the name of the missing dll or something?
I don't understand why the issue only happen with spyder. I tried with IPython Qt Console and it work. Does spyder use a embeded python version or something ?
I don't fully understand how dll shall be managed, I mean shall I provide dll like libGLESV2.dll with the .pyd or just give a path where to find it ?
Thank you in advance.

My guess
I think I find out which part of Qt/python is producing this issue, but I still don't know how to solve it.
My dll use signals/slots which need an event loop to be performed. If an event loop is already running the dll will try to use it, if the loop version (ex : PyQt5==5.14.1) isn’t the same as mine (ex Qt==5.15.1) import will be impossible.
Note that the reverse is true, if I run my dll an then try to start a loop with %gui qt the command will throw an error.
How to reproduce the issue :
Compile a Qt project available here.
Copy the output dll in the folder PyMyStack/dependencies of the VS Project (available here)
Compile the VS project.
Open an IPython console (without using qt has event loop)
Import the module created with VS (Import PyMyStack)
Run the magic command %gui qt
Last command shall print : ERROR:root:DLL load failed while importing QtSvg: The specified procedure could not be found.
How to hide/solve the problem:
Disclaimer : The solutions presented here are surely not the best, if you know a better one please share it ☺
If you just want to import your lib in Spyder, you can use another event loop. Here are the steps to change this:
In Spyder menus go to Tools→Preferences
Select “IPython console”
Go to “Graphics” tab and change the backend combo box to any other values than Qt or Automatic
If you want to use Qt event loop you will have to update it. You can do this with pip command, but remember than Spyder is not compatible with some version. Here is the pip command:
Pip install PyQt5==X.Y.Z
Where X and Y are the same version use to compile your Qt project. The last digit version seems to not be important.

How to install C++ dependencies "from source" for a Python package on Mac OS?

There is a Github repo containing Python "bindings" for a C++ library that I am interested in playing with. The README has abundant information about how to install the C++ library on Linux like machines, but no information about how to do so with a mac OS.
I have also opened up an issue requesting the README installation instructions include mac OS-specific installs in addition to linux. There hasn't been any activity on that issue.
Here are the two repos:
(Python) https://github.com/asiffer/python3-libspot
(C++) https://github.com/asiffer/libspot
Since the C++ package isn't available for installing via Brew/pip/anaconda, I'm not sure how to get going.
What I've Tried:
I have tried ./configure, and make. There is no ./configure file.
To address the lack of ./configure, read about a tool called autoconf which supposedly generates ./configure for you. I installed it with brew, but am not sure what arguments to pass it. These docs were pretty hard to understand: https://www.gnu.org/software/autoconf/manual/autoconf-2.67/html_node/Making-configure-Scripts.html
Just using make results in the error clang: error: unsupported option '-fopenmp'That sent me down a whole different rabbit hole which had me adding lines to the Makefile:
CPP = /usr/local/opt/llvm/bin/clang
CPPFLAGS = -I/usr/local/opt/llvm/include -fopenmp
LDFLAGS = -L/usr/local/opt/llvm/lib
omp_hello: omp_hello.c
$(CPP) $(CPPFLAGS) $^ -o $# $(LDFLAGS)
That felt dangerous because I have no idea what any of that stuff means. Plus it resulted in a new error: *** missing separator. Stop.
So then I read that's probably due to using "soft" tabs instead of "hard" tabs which can be identified using cat -e -t -v makefile_name. I found the one line where a "hard" tab was missing (the indented line above) and inserted it. This resulted in a new error:
make: *** No rule to make target `omp_hello.c', needed by `omp_hello'. Stop.
Next, following the advice of Yang Yushi and his follow on comments, I changed lines 39 and 40 according to his answer, plus added the locations of some additional files to the CXXFLAGS variable:
-I//opt/homebrew/Cellar/libomp/11.0.1/include
-L/opt/homebrew/Cellar/libomp/11.0.1/lib
And this got me a little further. Next, OSX didn't like where this script was trying to install, as explained by this answer. So I changed these two lines in the makefile which seemed to dictate install location:
INSTALL_HEAD_DIR = $(DESTDIR)/usr/include/libspot
INSTALL_LIB_DIR = $(DESTDIR)/usr/lib
to
INSTALL_HEAD_DIR = $(DESTDIR)/usr/local/include/libspot
INSTALL_LIB_DIR = $(DESTDIR)/usr/local/lib
And that indeed got me a little farther. Next I ran into an error complaining about the flat -t at these lines in the makefile:
#install -t $(INSTALL_LIB_DIR) $(LIB_DIR)/*.so
#install -t $(INSTALL_HEAD_DIR) $(INC_DIR)/*.h
So I deleted those flags, which then resulted in this error:
Checking the headers installation directory (/usr/local/include/libspot)
Checking the library installation directory (/usr/local/lib)
Installing the shared library (libspot.so)
install: /usr/local/lib: Inappropriate file type or format
For which I can find no reading material and have no clue how to fix. Any further assistance appreciated.
Here's a list of SO and other resources I've perused trying to answer this question:
Enable OpenMP support in clang in Mac OS X (sierra & Mojave)
makefile error: make: *** No rule to make target `omp.h' ; with OpenMP
makefile:4: *** missing separator. Stop
http://www.idryman.org/blog/2016/03/10/autoconf-tutorial-1/
https://www.gnu.org/software/autoconf/manual/autoconf-2.67/html_node/Making-configure-Scripts.html
https://developer.gnome.org/anjuta-build-tutorial/stable/create-autotools.html.en
My Question
How do I proceed.
If you know how to do this, could you also include a brief explanation of the concepts behind each step? I'd be happy to learn a little instead of just copying and pasting commands in the right order.

Compile the C++ source code with Apple Clang
I downloaded the prjoect (libspot) and successfully compiled it on my Mac. I change two lines (39 and 40) in the Makefile to make it work. (Following this answer)
CC = clang++ # change from g++ to default Apple clang
CXXFLAGS = -std=c++11 -Wall -pedantic -Xpreprocessor -fopenmp -lomp # additional flags
You should get the binary file by just type make with a "correct" Makefile.
(If you see something like "cant find omp.h", add -I/usr/local/opt/libomp/include to the CXXFLAGS.)
For the Question
The error message in the updated question description
make: *** No rule to make target omp_hello.c', needed by omp_hello'. Stop.
is telling us that the file omp_hello.c is missing. The Makefile is written to compile the source code omp_hello.c to an executable binary file omp_hello. If I have the C source file (omp_hello.c), the Makefile will allow me to compile by just typing
make
instead of
/usr/local/opt/llvm/bin/clang \
-I/usr/local/opt/llvm/include -fopenmp \
-L/usr/local/opt/llvm/lib \
omp_hello.c -o omp_hello
This is just a normal compile process, it has nothing to do with Python. The error message is saying the source code to be compiled (omp_hello.c) is missing.
It looks like this is a small project with custom Makefile. Normally you compile the code with just make. The error you got seems to suggest the lack of llvm. You may want to try install llvm following this answer.

Usually it comes to running brew install <your C++ package> or downloading the source code to some directory and running a set of commands:
./configure
make
make install
While usually it works, some packages can not be installed on Mac since their maintainers did not prepare configuration for Mac.

Can't "install" plpython3u - postgresql

I'm trying to use python language in postgresql. Something like this:
create or replace function test(_a integer) returns integer as $$
if _a%2==0:
return 'even'
elif _a%3==0:
return 'mult of 3'
else:
return _a
$$ language plpython3u
But when I run this, I get this error:
ERROR: language "plpython3u" does not exist
HINT: Use CREATE EXTENSION to load the language into the database.
SQL state: 42704
Then, I tried to create the extension of the python language by executing:
create extension plpython3u
Which tells me the following error:
ERROR: could not load library "C:/Program Files/PostgreSQL/12/lib/plpython3.dll": The specified module could not be found.
SQL state: 58P01
I checked if the plpython3.dll file is there. Then I read something about modifying the postgresql configure file by compiling postgres from the source code and adding --with python (I found some of this here).
My problem is that I don't know how to actually do this. My OS is windows server 2019 64 bits, python version is 3.7.4 and postgresql version is 12.2-1 (pgadmin 4.18).
How can I solve this?

Getting python to work with postgres seems to be version or versions dependent. I currently have postgres 9.6. and I had installed python 3.9. I had previously installed the extension plpython3u in postgres but time had gone by and I moved to another computer. When I tried to run a procedure based on Python, I got an error. I downloaded dependency walker, from here: https://www.opcsupport.com/s/article/How-do-I-figure-out-why-my-DLL-is-failing-Microsoft-Dependency-Walker or here: https://www.dependencywalker.com/. When I opened up the dependency walker, I dragged the plpython3.dll into the dependency walker, the .dll is located here: F:\pg96\lib. I then got the following screen -- below -- that seemed to indicate I needed to install a Python 3.7. I downloaded Python 3.7 from here: https://www.python.org/downloads/windows/. And my python procedures now worked.

No need to build from source, which would require that you install a C compiler, which is non-trivial on Windows.
You never told us if python3.dll was present in the directory or not, so I'll assume it was there. Then the error would indicate that a shared library that python3.dll links with is missing, most likely from Python 3. Installing Python 3 will probably solve the problem.

Cstdint Missing Error When Installing Pydaedalus with PiP

I am working on an application which involves route finding (a completely different subject), but for testing I need example mazes to test on. A colleague suggested I use pydaedalus to generate large scale mazes in the format I need. I am using the following code to try and install the module:
$pip3.6 install pydaedalus
This returns the following error:
-Wno-error=format-security
In file included from daedalus/_maze.cpp:467:
In file included from daedalus/wrapper.h:8:
daedalus/src/util.h:31:10: fatal error: 'cstdint' file not found
#include <cstdint>
^
1 error generated.
error: command '/usr/bin/clang' failed with exit status 1
I have done some research and have found nothing which addresses this. I have also done some (limited) C++ development using cstdint, which has always worked.
I came across this question, but it appears to address a separate issue.
I am developing in OSX 10.10.5
Any help that you can provide is much appreciated!

These compile errors are down to daedalus's requirement of the C++11 standard, which is sometimes a bit tricky to get working on Mac OS X. One idea might be to check to make sure your Xcode is completely up to date.
The page you linked also suggests to try linking against clang's standard library instead of the GCC standard library. I'm not sure if this will work, or if it will give you linking errors on build or when you import daedalus into python, but you could give it a shot anyway:
CFLAGS='-stdlib=libc++' pip3.6 install pydaedalus
Another idea would be to encourage pip to use the clang++ frontend, which your link also suggests might help. You should be able to set this with the environment variable CXX (or, just possibly, CC).
CXX=clang++ pip3.6 install pydaedalus
Try various combinations of those environment settings (e.g., CXX and CFLAGS), and hopefully something will work eventually.

compiling Cython with MinGW - undefined reference PyExc

I'm trying to compile a simple code snippet from the book "Cython - A guide for Python programmers", and when i compile, i get the following error:
H:\Cython>python setup.py build_ext -i --compiler=mingw32
running build_ext
building 'fib' extension
C:\MinGW\bin\gcc.exe -mdll -O -Wall -IC:\Anaconda3\include -IC:\Anaconda3\include -c fib.c -o build\temp.win32-3.4\Release\fib.o
writing build\temp.win32-3.4\Release\fib.def
C:\MinGW\bin\gcc.exe -shared -s build\temp.win32-3.4\Release\fib.o build\temp.win32-3.4\Release\fib.def -LC:\Anaconda3\libs -LC:\Ana
conda3\PCbuild -lpython34 -lmsvcr100 -o H:\Cython\fib.pyd
build\temp.win32-3.4\Release\fib.o:fib.c:(.text+0xb6): undefined reference to `_imp__PyExc_TypeError'
build\temp.win32-3.4\Release\fib.o:fib.c:(.text+0xf3): undefined reference to `_imp__PyExc_TypeError'
build\temp.win32-3.4\Release\fib.o:fib.c:(.text+0x3cc): undefined reference to `_imp___PyThreadState_Current'
build\temp.win32-3.4\Release\fib.o:fib.c:(.text+0x857): undefined reference to `_imp__PyExc_NameError'
build\temp.win32-3.4\Release\fib.o:fib.c:(.text+0xa55): undefined reference to `_imp__PyExc_ImportError'
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: build\temp.win32-3.4\Release\fib.o: bad reloc address 0x0 in s
ection `.data'
collect2.exe: error: ld returned 1 exit status
error: command 'C:\\MinGW\\bin\\gcc.exe' failed with exit status 1
H:\Cython>
setup.py:
from distutils.core import setup
from Cython.Build import cythonize
setup(ext_modules=cythonize('fib.pyx'))
fib.pyx:
def fib(int n):
cdef int i
cdef double a=0.0, b=1.0
for i in range(n):
a, b = a + b, a
return a
When I google this problem, others who have had the error had a mix between 32 and 64 bit stuff, I'm not doing that.

I sat down and looked the errors over again today, and found the issue.
The problem is that I used Anaconda rather than compiling everything from scratch myself - that means that some Cython components were compiled with MSVC. As above you can see that I'm trying to use MinGW to compile the Cython test script. Why mixing compilers like that doesn't work is outside my scope of knowledge, but it doesn't. Compiling my Cython test scripts with MSVC works.
(use Visual Studio C++ 2008/2010 for python 2.x/3.x respectively)
As for the reason that I attempted to use MinGW (against standard recommendation) was that my msiserver service had somehow broken (I'm on an old laptop, so i don't recall the reason), and was hoping to find a quick way out, rather than fixing the msiserver service.
The fix for the msiserver service is pretty unrelated to this question, but it was rather hard to find, so i figured I'd link and mirror it here:
http://www.vistax64.com/vista-installation-setup/96680-repair-windows-installer-service-vista-all-versions.html
For all those unfortunate souls searching and Googling for how to
repair the Windows Installer Service, I have some info for you. A
couple days ago I tried to uninstall one of my apps and stalled on an
error "Windows Installer Service cannot be accessed". After many
trials and errors trying to fix this issue, I stumbled upon a new fix
for this issue that has worked in all these situations where the
Windows Installer Service will not manually start and in essense, not
allow install or uninstall tasks to complete.
Here's the easy steps:
1. Go to a Windows Vista (Any Version) computer that has the Windows
Installer service running correctly and run regedit(Start-Run-Regedit)
2. Go to the location
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\msiserver
3. Right click on this key and select "Export" and save the key to a Flash
Drive or other.
4. Run sfc /scannow on the damaged Vista computer - you won't need the
install disk as it goes to backup files on your HD. Do not reboot when
complete
5. Double click saved .reg file from working machine and import registry
settings into damaged Vista computer.
6. Now reboot and try to install/uninstall
If many of you have success with this method, please post this fix
around the WWW as I went through over 1000 links with users having the
same problem and not being able to solve it. Shame on Microsoft, very
sloppy. It would have been so nice if Microsoft released Windows
Installer 4.0 as a standalone installation with Vista's release so I
could have repaired it, most users have been doing fresh installs to
fix this. Get your act together Microsoft!!!!
The CAT
Thank you, the cat.