Run python script in Qt

[NotYourFan]

Hey,

im trying to run a python Script in Qt after clicking a button, with the following Code:

void TestWindow::loadFile()
    QProcess p;
    QStringList params;

    params << "createJSON.py";
    p.start("python.exe", params);
    p.waitForFinished(-1);
    QString p_stdout = p.readAll();

i get the following error:

1. Process started!
2. Error occurred "Process crashed"
3. OUT ""
4. ERR "Fatal Python error: initfsencoding: unable to load the file system codec\nModuleNotFoundError: No module named 'encodings'\n\nCurrent thread 0x00005b50 (most recent call first):\n"

If i run the script in my python IDE it works fine.
My "createJSON.py" create a JSON-File so i can checked if the Qt run my script successfully.

Do you have any idea how i can run otherwise a python script in qt?

[closx]

I think it is a internal python error.
According to Jayground said here, you can try to check Add Python to environment variables selection on advanced options when custom installation of the Python.

[NotYourFan]

i reinstalled python and checked the variables … all fine.
And as i said, when i run the Script with cmd ( cmd -> python.exe "path/createJSON.py") it works perfect

[J.Hilk]

@NotYourFan
well, have you tried giving QProcess the absolute path to the python file, as you did in your cmd prompt ?

[NotYourFan]

yes of coruse, like:

void TestWindow::loadFile()
    QProcess p;
    QStringList params;

    params << "createJSON.py";
    p.start("C:/development/Python/Python37/python.exe", params);
    p.waitForFinished(-1);
    QString p_stdout = p.readAll();

[J.Hilk]

@NotYourFan said in Run python script in Qt:
I actually meant the absolute path to

createJSON.py

I assume createJSON.py is inside your project folder and you start the program via QtCreator but, the created exe is not in your project folder -> so it can't find the python script

[NotYourFan]

Sry @J-Hilk i missunderstood.

But i try this also …

like:

void TestWindow::loadFile()
    QProcess p;
    QStringList params;

    params << "C:/development/Qt/ProjektXY/createJSON.py";
    p.start("C:/development/Python/Python37/python.exe", params);
    p.waitForFinished(-1);
    QString p_stdout = p.readAll();

i´m desperately … i dont know what to do, i try everything.

[J.Hilk]

@NotYourFan since you're on windows, you're using the wrong path separator

[NotYourFan]

@J-Hilk whats the Right path separator?

[J.Hilk]

@NotYourFan
https://en.wikipedia.org/wiki/Filename#Reserved_characters_and_words

---

backslash or probably double backslash

[NotYourFan]

This post is deleted!

[NotYourFan]

okay, thx for your Suggestion.

void TestWindow::loadFile()
    QProcess p;
    QStringList params;

    params << "C:\\development\\Qt\\ProjektXY\\createJSON.py";
    p.start("C:\\development\\Python\\Python37\\python.exe", params);
    p.waitForFinished(-1);
    QString p_stdout = p.readAll();

i tried one time with Backslash and one time with double Backslash … same Problem.

[jsulm]

@J.Hilk said in Run python script in Qt:

since you're on windows, you're using the wrong path separator

With Qt / should work on Windows as well, shouldn't it?

[J.Hilk]

@jsulm I'm unsure

usually yes, but in this case you're trying to start a System program from the OS. Until now, I've always only used it to start an external program, that I shipped with the other Qt installation and therefore was always at the same depth as the main executable or it was on a unix system...

@NotYourFan
have you seen this thread ?
https://stackoverflow.com/questions/15127047/qt-calling-external-python-script

It may help you

[aha_1980]

@jsulm

With Qt / should work on Windows as well, shouldn't it?

It is really important to use forward slashes for Qt functions, yes. However, the parameter for python (the path to the script) is not evaluated from Qt but from the python interpreter, so here backslashes might be needed.

That gives:

params << "C:\\development\\Qt\\ProjektXY\\createJSON.py";
p.start("C:/Development/Python/Python37/python.exe", params);

Looks funny, though.

p.waitForFinished(-1); I would use a SLOT here.

And for testing: can you just try python -c 'print "Hello World"' first?

[aha_1980]

@J.Hilk said in Run python script in Qt:

usually yes, but in this case you're trying to start a System program from the OS

As said, the path for QProcess should work with forward slash. The path for the parameter (the script) probably not.

[NotYourFan]

@J-Hilk thank you for the stackoverflow link, i've seen it and try it.
@aha_1980 i test python -c 'print "Hello World"' --> i get Nothing.

[aha_1980]

@NotYourFan said in Run python script in Qt:

@aha_1980 i test python -c 'print "Hello World"' --> i get Nothing.

How did you test it?

[NotYourFan]

put python -c 'print "Hello World"' in p.start

[Pablo J. Rogina]

@NotYourFan just in case, you may want to use Python embedded in your Qt application...

[jsulm]

@NotYourFan It doesn't work like this. You have to put the command as first parameter to start() and all parameters for the command as parameter list.

[Gojir4]

@jsulm Are you sure about that ?
from Qt Doc:

QProcess process;
process.start("del /s *.txt");

[NotYourFan]

@jsulm i readed in the Qt Doc.
@Gojir4 you are right.
@Pablo-J-Rogina thx for your Suggestion … but i should / want to do it with QProcess …

[SGaist]

Hi,

@NotYourFan just in case, did you try to compare the environment variables of your QProcess object and the one you have when running e.g. from a terminal ?

@Gojir4 You are right about that specific overload, but the documentation also states that this overload should be avoided if possible.

[Gojir4]

@SGaist My bad. Thanks for clarification !

[JonB]

@NotYourFan
I am lost as to where you are now.

Assuming it's still crashing --- is that right? --- surely you want to break it down to simplify now. Start with:

    params << "-V";
    p.start("C:\\development\\Python\\Python37\\python.exe", params);
    p.waitForFinished(-1);
    QString p_stdout = p.readAll();

What exactly happens?

[NotYourFan]

@JonB, i get a error Message: ….

ModuleNotFoundError: No module named 'encodings'

[JonB]

@NotYourFan
OK! So, you can forget about your createJSON.py script and anything it does.

I don't know why you get this when spawning from Qt but not when running your python.exe directly from a command prompt. Either it's something to do with it sending output to a pipe you are reading from, or it's to do with your general Python environment being different between the two situations.

You want now to Google for python ModuleNotFoundError: No module named 'encodings'. There are posts/suggestions. Looks to me like it might be to do with whether you are using a virtual environment or not, but I'm sure one of the hits will sort you out....

[aha_1980]

@JonB I can imagine that the Environment inside Qt Creator is different (e.g. PATH) and therefore other (incompatible) executables and libraries are found.

@NotYourFan: You should carefully check the Run Environment variables inside Qt Creator, especially PATH. That's all I can say for now.

Regards

[NotYourFan]

@JonB, when i run my createJSON.py from the console, everything working fine.
@aha_1980 thanks !! I will checked immediately.

[NotYourFan]

@aha_1980 !!!!!
Thank you :=)

That was the Problem.
I use for "Debug" MinGW (MinGW included python2.7 and set a PYTHON variable)
So now i tried like this:

QProcess cmd;
QProcessEnviroment env = QProcessnviroment::systemEnviroment();
QProcessEnviroment envUpdate;

envUpdate.inser("PATH", env.value("PATH"));
cmd.setProcessEnviroment(envUpdate)
cmd.start("python.exe C:\\Users\\...\\Desktop\\...\\createJSON.py")
cmd.waitForFinished();

Now it works :)

Thank you @all for your standby