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Python support for Qt dll

I have my own C++ library project(with source) written in Qt and it uses QTcpsocket, QUdpSocket, QSerialPort signals and slots.
I would like to support this library in Python as well.
What is the preferred way to do this?
Writing a wrapper in Python, if so does it have obstacles?
Dont know if PyQt is just for this purpose?
Or do you thnink is it better to rewrite the lib in Python by just implementing the logic used in C++ library project.
As this is library is part of a SDK, same applies for supporting QT dll with .NET as well in fact, as a second step after supporting Python.
Example API of Qt.
quint16 SendCommandAsync(CmdBaseSpv1* pcommand,
ConnectionArg connectionArg,
emitLogOptions::emitLogOption logOption,
LogInfo &txLogInfo,
LogInfo &rxLogInfo);
I want to call this function from Python.
Function parameters CmdBaseSpv1, ConnectionArg, emitLogOption, LogInfo are all Qt classes.
Some of these arguments are using the QOBJECT base class.
As you see from the function name; it is an Asynchronous function call. Result will emit a signal so I need to get async result as well.

I'll write down what I know about wrapping C++ libraries and will try to source it, but as a huge disclaimer, I have only used this for something very, very simple myself.
You ask about rewriting the library in Python. I would say this depends. If the code is trivial, then I don't see why not. If it is larger and has to be kept up-to-date with other code (as you imply with .Net), I wouldn't. It makes sense to reuse the same code for both.
 My suggestion
From what I see of your code I would try to wrap it using boost::python or SWIG.
How to wrap
The main trouble is going to be to create CmdBaseSpv1, ConnectionArg, etc. in Python.
If you don't need any Qt-classes to instantiate your classes, this should be straightforward. However, in case you need the Qt types inside of Python (e.g. because the constructor of CmdBaseSpv1 requires a QString), your task is a lot more complicated because you need a way to convert a Python-string into a QString. If you can, you should only use stl-types.
Everything in Python
The simplest way to wrap a small C library is to use the cffi module (or ctypes). You can write the full binding in Python. However, this is a lot of manual work if your API is large and can get difficult.
There is another problem: ctypes is only compatible with C, not C++. So you'd need to change your interface to be compatible with C, internally you could still use C++ and Qt.
Wrap by hand
An alternative is to wrap the library calls yourself. You can either do this by using the Python API. There are also a few libraries that help you create the bindings. Boost::python seems especially promising and works with C++.
Binding generators
If your API is very large, you should use a binding generator which parses the C++ code and generates the bindings itself. For example sip is one of them. It is used to create the bindings for the whole Qt library. There are a few binding generators out there, one mentioned in the Python docs is SWIG. PySide uses Shiboken and also has a nice description of it on their website.
SWIG has the additional advantage, that you can create bindings for multiple languages, including C#.
PyQt
PyQt is a binding generated from Qt using sip. You'll probably not need it, unless you need to access the full power of Qt from inside Python. If this is the case, consider using sipfor generating the bindings, so things like the signal-slot mechanism are compatible between your library and PyQt.
Challenges with bindings
Bindings come with a few challenges because Python and C++ are different in some key areas.
Memory-management
Memory management in Python is almost automatic, in C++ you're required to do it manually. For example
def myfunc():
mywidget = QWidget()
at the end of myfunc() mywidget gets garbage collected. In C++ however
void myfunc() {
auto mywidget = new QWidget();
}
mywidget is still around. This means that even when inside Python, you need to take care of the C++ memory management. The problems I've seen are memory leaks and dangling pointers. Watch out for this when using callbacks, you don't want Python to garbage collect the callback while C++ thinks it's still alive.
Exceptions
Not all programming languages have exceptions or deal with them the same way. For example, it would be nice if an exception inside C++ can be caught inside Python.
Links to related question
How to wrap a c++ library for python? (example of boost::python)
Exposing a C++ API to Python (discussion about boost::python, SWIG and more)
https://stackoverflow.com/a/5686873 (discusses Cython, another choice)

Wrap Scala library in Python

There is a Scala library I'd like to use, namely BIDMach, however I need to be able to use it from Python rather than in Scala. I've been trying to think of different ways of possible being able communicate between the library and Python code, such as creating an HTTP server in Scala and calling this from Python, using something like JPype to try and use Scala libraries in Python, and different types of interprocess communication. However, none of them seem to work very well, and would seem to require a large amount of reimplementation of what is already in the library. Does anyone know of a good way of going about this?
edit: In terms of exactly what I think I'd like to do, ideally I'd be able to get close to almost all of the libraries functionality usable in Python, however that probably isn't realistic. It would be nice if some of the Scala classes were easily usable in Python, without too much repeated implementation effort. The reason I don't think what I've looked into so far will work well is because it requires a fair bit of reimplementation of what is already in the library (i.e. representing something like a matrix in JSON, as a way of transporting data to/from Python/Scala)

Using python modules in node.js

Is it possible to create a glue that makes it possible for python modules (more specifically, library bindings) to be used in node.js? Some of the data structures can be directly mapped to V8 objects - e.g. array, dict.
More importantly - would that be a more elegant way to create bindings than manually or through FFI. In short, would it be worth it?

Try this node.js module, that is a bridge: Node-Python,
NOTE: The Project is 7 years old and still stuck at v0.4. A lot of functionality like converting between Python and Node arrays is still missing. It may be safe to assume that it's no longer supported by its original author(s)

Edge.js does a fine job at this. It allows you to write a Python script and then call the routines from Node.js, which can be used to easily create bindings with python modules.

Communicate with another program using subprocess or rpc / rest in python?

I have a situation where there is a program which is written in c++. It is a kind of a server which you need to start first. Then from another konsole you can call the program passing commandline arguments and it does stuff. Also it provides rpc and rest based access. So you can write a rpc or rest based library to interface with the server.
So my question is, since the program can be managed using mere commandline arguments, isn't it better to use python's subprocess module and build a library (wrapper) around it? Or is there any problem with this method?
Consider another case. Say I wanted to build a GUI around any linux utility like grep which allows user to test regular expressions (like we have on websites). So isn't it easier to communicate to grep using subprocess?
Thanks.

I think I'd prefer to use any of the rpc or rest interfaces, because the results you can obtain from them are usually in a format that is easy to parse since those interfaces have been designed for machine interaction. However, a command line interface is designed for human interaction and this means that the output is easy to parse for the human eye, but not necessarily by another program that receives the output.

Is it possible to use re2 from Python?

i just discovered http://code.google.com/p/re2, a promising library that uses a long-neglected way (Thompson NFA) to implement a regular expression engine that can be orders of magnitudes faster than the available engines of awk, Perl, or Python.
so i downloaded the code and did the usual sudo make install thing. however, that action had seemingly done little more than adding /usr/local/include/re2/re2.h to my system. there seemed to be some *.a file in addition, but then what is it with this *.a extension?
i would like to use re2 from Python (preferrably Python 3.1) and was excited to see files like make_unicode_groups.py in the distro (maybe just used during the build process?). those however were not deployed on my machine.
how can i use re2 from Python?
update two friendly people have pointed out that i could try to build DLLs / *.so files from the sources and then use Python’s ctypes library to access those. can anyone give useful pointers how to do just that? i’m pretty much clueless here, especially with the first part (building the *.so files).
update i have also posted this question (earlier) to the re2 developers’ group, without reply till now (it is a small group), and today to the (somewhat more populous) comp.lang.py group [—thread here—]. the hope is that people from various corners can contact each other. my guess is a skilled person can do this in a few hours during their 20% your-free-time-belongs-google-too timeslice; it would tie me for weeks. is there a tool to automatically dumb-down C++ to whatever flavor of C that Python needs to be able to connect? then maybe getting a viable result can be reduced to clever tool chaining.
(rant)why is this so difficult? to think that in 2010 we still cannot have our abundant pieces of software just talk to each other. this is such a roadblock that whenever you want to address some C code from Python you must always cruft these linking bits. this requires a lot of work, but only delivers an extension module that is specific to the version of the C code and the version of Python, so it ages fast.(/rant) would it be possible to run such things in separate processes (say if i had an re2 executable that can produce results for data that comes in on, say, subprocess/Popen/communicate())? (this should not be a pure command-line tool that necessitates the opening of a process each time it is needed, but a single processs that runs continuously; maybe there exist wrappers that sort of ‘demonize’ such C code).

David Reiss has put together a Python wrapper for re2. It doesn't have all of the functionality of Python's re module, but it's a start. It's available here: http://github.com/facebook/pyre2.

Possible yes, easy no. Looking at the re2.h, this is a C++ library exposed as a class. There are two ways you could use it from Python.
1.) As Tuomas says, compile it as a DLL/so and use ctypes. In order to use it from python, though, you would need to wrap the object init and methods into c style externed functions. I've done this in the past with ctypes by externing functions that pass a pointer to the object around. The "init" function returns a void pointer to the object that gets passed on each subsequent method call. Very messy indeed.
2.) Wrap it into a true python module. Again those functions exposed to python would need to be extern "C". One option is to use Boost.Python, that would ease this work.

SWIG handles C++ (unlike ctypes), so it may be more straightforward to use it.

You could try to build re2 into its own DLL/so and use ctypes to call functions from that DLL/so. You will probably need to define your own entry points in the DLL/so.

You can use the python package https://pypi.org/project/google-re2/. Although look at the bottom, there are a few requirements to install yourself before installing the python package.