bad3.py

import io
import sys

import PyQt5.QtCore
import PyQt5.QtWidgets
import PyQt5.uic
import sip


system_info = f'''\
sys.version: {sys.version}
sys.platform: {sys.platform}
QT_VERSION_STR: {PyQt5.QtCore.QT_VERSION_STR}
PYQT_VERSION_STR: {PyQt5.QtCore.PYQT_VERSION_STR}
SIP_VERSION_STR: {sip.SIP_VERSION_STR}'''


ui_text = '''\
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>Form</class>
 <widget class="MyWidget" name="Form">
  <layout class="QVBoxLayout" name="layout">
  </layout>
 </widget>
 <customwidgets>
  <customwidget>
   <class>MyWidget</class>
   <extends>QWidget</extends>
   <header>bad3</header>
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>
'''

class MyWidget(PyQt5.QtWidgets.QWidget):
    pass


def main():
    print(system_info)
    app = PyQt5.QtWidgets.QApplication([])

    Ui, UiBase = PyQt5.uic.loadUiType(io.StringIO(ui_text))


if __name__ == '__main__':
    main()


    #exec(code_string.getvalue(), ui_globals)
    #ui_base = ui_globals.get(winfo["baseclass"])
    #if ui_base is None:
        #ui_base = getattr(QtWidgets, winfo["baseclass"])
    #return (ui_globals[winfo["uiclass"]], ui_base)

out

 ~/st.src   boots ●  venv/bin/python bad3.py
sys.version: 3.7.4 (default, Aug  2 2019, 12:58:45) 
[GCC 6.3.0 20170516]
sys.platform: linux
QT_VERSION_STR: 5.13.0
PYQT_VERSION_STR: 5.13.0
SIP_VERSION_STR: 4.19.18
Traceback (most recent call last):
  File "bad3.py", line 50, in <module>
    main()
  File "bad3.py", line 46, in main
    Ui, UiBase = PyQt5.uic.loadUiType(io.StringIO(ui_text))
  File "/home/altendky/st.src/venv/lib/python3.7/site-packages/PyQt5/uic/__init__.py", line 204, in loadUiType
    return (ui_globals[winfo["uiclass"]], getattr(QtWidgets, winfo["baseclass"]))
AttributeError: module 'PyQt5.QtWidgets' has no attribute 'MyWidget'