[PySide] Python bindings for Qt/C++ library (advice needed on best practices)

info at mycontent.gr info at mycontent.gr
Thu Jul 19 02:10:35 CEST 2018

Dear all,

first of all congratulations and thanks to the PySide2 team for a great 

After going through the blog post at 
http://blog.qt.io/blog/2018/05/31/write-python-bindings/ on creating 
Python bindings for a C++ library with Shiboken, a few questions arise 
when thinking about a bigger/real-life project. I suspect these 
questions will come up frequently as people try to build Python bindings 
for their projects, so I would like to volunteer to collect the answers 
that I hope to get from this mailing list into a tutorial-style document 
(if the team is interested in this!)

Suppose that we have a Qt-based C++ library, for which we would like to 
create Python bindings.
Many library classes are subclasses of QObject. There are several 
methods accepting QString arguments and returning QLists, QHashes, 
QMaps, as well as pointers to the library’s objects.
Suppose that the library uses QtSql and QtXml (and many elements of 
QtCore) internally, but these objects need not be exposed to the user.
In most use cases, the users of the bindings will not need the Qt user 
interface classes, as they will be writing automation scripts. The 
library itself does not depend on QtGui, QtWidgets etc.

What would be the best course of action:
1. Write a thin interface layer to the library using only C++ primitives 
and STL types, like std::string, std::list, so that all interfaces that 
will be exposed to Python accept and return standard library constructs?
2. Create Python bindings with Qt objects as arguments?

In the first case, how can we keep the dependencies for library users to 
a minimum? QtCore, QtSql and QtXml are necessary for the functioning of 
the library, but the Python bindings of these Qt libraries, normally 
should not be necessary (is this correct?).
In the second case, how can we package the library in such a way that 
the required PySide2 dependencies are installed automatically 
(preferably using pip)? How can we keep the dependencies to a minimum?

Thank you very much for your time!

Kind regards,

George Christodoulides

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