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I would like to embed Python interpreter in to a Qt 5 application.

I have a working application in Qt 5 but when I put

#include <Python.h>

at the top (below Qt headers) the compilation breaks with

../sample/python3.3m/object.h:432:23: error: expected member name or ';' after declaration specifiers
PyType_Slot *slots; /* terminated by slot==0. */
~~~~~~~~~~~       ^

When I put Python header above the Qt headers it breaks with

In file included from ../Qt5.0.1/5.0.1/clang_64/include/QtGui/QtGui:59:
../Qt5.0.1/5.0.1/clang_64/include/QtGui/qpagedpaintdevice.h:63:57: error: expected '}'
                    A0, A1, A2, A3, A5, A6, A7, A8, A9, B0, B1,
                                                        ^
/usr/include/sys/termios.h:293:12: note: expanded from macro 'B0'
 #define B0      0
                ^
../Qt5.0.1/5.0.1/clang_64/include/QtGui/qpagedpaintdevice.h:62:19: note: to match this '{'
    enum PageSize { A4, B5, Letter, Legal, Executive,
                  ^
1 error generated.

Please, does anyone know why this happens? I could be because Qt and Python define some common words? What can I do about it?

Ecir Hana
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2 Answers2

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This happens because including Python.h first indirectly includes termios.h, which defines B0 to be 0, which in turn qpagedpaintdevice.h want's to use as a variable name. Including Python.h after the Qt includes does pretty much the same thing the other way around with the string 'slots'.

I suggest the following order:

#include <Python.h>
#undef B0
#include <QWhatEver>
axxel
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  • Unfortunately this did not work for me as I was developing a Qt Plugin and many files included Qt headers already. This solution was the best for my use case: https://stackoverflow.com/a/49359288/4085930 – AGK Nov 26 '20 at 11:02
7

An alternative to the accepted answer:

Since Qt uses the slots as a reserved keywords there is a clash with the declaration of the slots member of the PyType_Spec struct in the Python API.

Qt can be instructed to not use the normal moc keyword, and this will remove the clash. This is done by adding the following to your project file: CONFIG += no_keywords

The drawback is then that you will need to refer to the corresponding Qt macros instead of the previous keywords.

Thus the following replacements will be needed for the Qt side: signals -> Q_SIGNALS slots -> Q_SLOTS emit -> Q_EMIT

This is explained in the Qt docs on signals and slots on the section Using Qt with 3rd Part Signals and Slots.

PS: This is normally a good option when starting a new project, not when adding Python to an existing code base that uses the Qt keywords extensively.

CJCombrink
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    If you are not using qmake see https://stackoverflow.com/questions/46571438/turning-the-no-keyword-qt-option-on-in-a-cmake-file-to-work-with-boostsignal/46573144 for how to set the no-keyword option. – plugwash Jun 02 '20 at 16:33