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Complete newbie to Qt and Qt Designer. I tried following some tutorials online to figure a way to embed matplotlib graph in Qt. Apparently the approach is to use subclass of QWidget which is done by "promoting" the QWidget.

I tried the approach shown in this SE link and this youtube video

Without promoting the QWidget, the *.ui file can be loaded into python without having any issue with the below script.

from PyQt5 import QtWidgets, uic
import sys

class Ui(QtWidgets.QMainWindow):
    def __init__(self):
        super(Ui, self).__init__()
        uic.loadUi('untitled.ui', self)
        self.show()

app = QtWidgets.QApplication(sys.argv)
window = Ui()
app.exec_()

But when I promote the QWidget as below, I get the following error.

enter image description here

Traceback (most recent call last):
  File "C:\Users\user.user\Desktop\pyqt_gui.py", line 11, in <module>
    window = Ui()
  File "C:\Users\user.user\Desktop\pyqt_gui.py", line 7, in __init__
    uic.loadUi('untitled.ui', self)
...
...
...
  File "C:\Users\user.user\Anaconda3\lib\site-packages\PyQt5\uic\Loader\qobjectcreator.py", line 115, in search
    module = __import__(mname, {}, {}, (cls,))
ModuleNotFoundError: No module named 'canvas'

Could someone please shed some light on this ?

ekhumoro
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XYZ
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1 Answers1

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It seems the guides you followed don't explain clearly enough how to link the promoted widget to your Canvas class, since your screenshot shows the wrong values. When you first enter the Promoted class name in the Promoted Widgets dialog, Qt Designer will automatically fill in the Header file, so it will end up looking like this:

screenshpt

But this is intended to work with C++ projects rather than Python ones, so you need to change "canvas.h" to the import path of the Python module that contains your Canvas class. Thus, if that module is called "canvas.py" and is in the same folder as your "pyqt_gui.py" file, you would simply need to edit the Header file to "camvas" (i.e. without the extension). To fix your existing ui-file, you can re-open the Promoted Widgets dialog and then double-click the current header-file value to edit it (and then also make sure you save the changes afterwards):

screenshot

This will result in the following line being added to the generated Python module:

from canvas import Canvas

(If you want to preview this in Qt Designer, you can select Form -> View Python Code in the menu-bar).

NB: you can enter any valid Python import path as the Header file. So if your custom widget module was in a sub-package called "widgets", you could enter "widgets.canvas" instead. In addition, it's also possible to use relative imports by specifying the base-package via an argument to loadUi. In that scenario, you would enter ".canvas" (note the leading dot) as the Header file, and then call loadUi like this:

uic.loadUi('untitled.ui', self, package='widgets')
ekhumoro
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  • Thanks very much, but this didnt work. I added a path to the Header file field and saved the canvas file. and used sys.path.append('C:/Users/.../Desktop') so that python can import it. when compiled my ui file look like below def retranslateUi(self, MainWindow): _translate = QtCore.QCoreApplication.translate MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow")) from C:\Users\...\Desktop\canvas import Canvas – XYZ May 31 '22 at 02:48
  • @m2as3registeredservicesohmone As I stated very clearly in my answer, you only need to enter "canvas" (i.e. exactly as is shown in the second screenshot). This will result in the line `from canvas import Canvas` being added to the generated module. Also, you ***do not*** need to modify `sys.path` in any way. Please read my answer more carefully and make sure you follow the advice given there. (And note that the section at the bottom below the line is *optional additional information*, so you can ignore that for the moment). – ekhumoro May 31 '22 at 09:22
  • Hi @ekhumoro, Tried it again and it worked as you stated. Thanks heaps. – XYZ Jun 01 '22 at 01:42