Why Can't I use the varible name delclass?

Question

I'm making a calender using pyqt5, and it gives me this error when I Wrote these lines of code: from pyqt5 import QtCore, QtGui, QtWidgets, uic, and delclass = uic.loaduiType.

Traceback (most recent call last):
  File "C:\Users\hungy\Desktop\Mason Works\Python\Projects\Calender.py", line 7, in <module>
    delclass = uic.loadUiType('Del_btn.ui')
  File "C:\Users\hungy\AppData\Local\Programs\Python\Python39\lib\site-packages\PyQt5\uic\__init__.py", line 204, in loadUiType
    exec(code_string.getvalue(), ui_globals)
  File "<string>", line 5
    def setupUi(self, del):
                      ^
SyntaxError: invalid syntax

What's wrong with my code? I tried Changing the name to Delclass, but that didn't work. This is my code:

import sys
from PyQt5 import QtCore, QtGui, QtWidgets, uic

# defines the formclasses
calclass = uic.loadUiType("Calender.ui")[0]
addclass = uic.loadUiType('Add_btn.ui')
delclass = uic.loadUiType('Del_btn.ui')
editclass = uic.loadUiType('Edit_btn.ui')
# classes
class Add(QtWidgets.QMainWindow, addclass):
    def __init__(self, parent=None):
        QtWidgets.QMainWindow.__init__(self, parent)
        self.setupUi(self)
        # self.Namevalue = Name_Text.value

class Calender(QtWidgets.QMainWindow, calclass):
    def __init__(self, parent=None):
        QtWidgets.QMainWindow.__init__(self, parent)
        self.setupUi(self)
        self.Add.triggered.connect(self.add_clicked)
        self.Delete.triggered.connect(self.del_clicked)
        self.Close_Exit.triggered.connect(self.x_clicked)

    def x_clicked(self):
        self.close()

    def del_clicked(self):
        pass

    def add_clicked(self):
        pass

app = QtWidgets.QApplication(sys.argv)
Window = Calender()
Window.show()
app.exec_()

.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>del</class>
 <widget class="QDialog" name="del">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>355</width>
    <height>106</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Del</string>
  </property>
  <property name="sizeGripEnabled">
   <bool>false</bool>
  </property>
  <widget class="QDialogButtonBox" name="OKCANCEL">
   <property name="geometry">
    <rect>
     <x>-80</x>
     <y>60</y>
     <width>341</width>
     <height>32</height>
    </rect>
   </property>
   <property name="orientation">
    <enum>Qt::Horizontal</enum>
   </property>
   <property name="standardButtons">
    <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
   </property>
  </widget>
  <widget class="QPushButton" name="Why">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>10</y>
     <width>93</width>
     <height>28</height>
    </rect>
   </property>
   <property name="text">
    <string>Why:</string>
   </property>
  </widget>
  <widget class="QPlainTextEdit" name="plainTextEdit">
   <property name="geometry">
    <rect>
     <x>120</x>
     <y>10</y>
     <width>191</width>
     <height>31</height>
    </rect>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections>
  <connection>
   <sender>OKCANCEL</sender>
   <signal>accepted()</signal>
   <receiver>del</receiver>
   <slot>accept()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>248</x>
     <y>254</y>
    </hint>
    <hint type="destinationlabel">
     <x>157</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
  <connection>
   <sender>OKCANCEL</sender>
   <signal>rejected()</signal>
   <receiver>del</receiver>
   <slot>reject()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>316</x>
     <y>260</y>
    </hint>
    <hint type="destinationlabel">
     <x>286</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
 </connections>
</ui>

Answer 1

From the look of your code, you probably renamed the top level widget in Qt Designer as del.

While this doesn't represent a real problem from the Qt perspective, it can become such when using uic functions, which build a raw python file (or an "abstract" form of it) when using loadUiType.

uic (and pyuic, which uses the same functions) creates functions and objects based on the object names of the UI. Among these, there are:

• def setupUi(self, <object name of the form>);
• def retranslateUi(self, <object name of the form>);

The result is that if you name del your top level object, the functions will be:

• def setupUi(self, del);
• def retranslateUi(self, del);

This will obviously cause an exception, since del cannot be used like that in python.

Be aware that the same is valid for all other python protected words:

• exec (while this is not an issue anymore in recent python versions, it's still better to avoid it, similarly to print)
• raise, assert
• def, class
• if, elif, else, not
• for, while
• continue, break
• try, except, finally
• etc...

The solution (which is valid in any case) is to carefully choose object names: look for descriptive names, not short names, as they don't have any practical benefit.
Instead of del, prefer delButton (or del_button, if you want to keep the standard Python style), or deleteButton.

Remember: the name reference (or object name in Qt) of an object should always allow you to tell at a glance what that object is and what it does.
What does "del" do? Delete? Delete what? Is it a function or a variable? Is it a widget? If it's a widget, what kind of widget is it?

Reopen the UI file in Designer and change the name of the top level object accordingly, and also ensure that no other widget uses those protected names, because they would throw an exception in any case (for instance, you cannot have an object named self.raise).

Answer 2

del is a reserved word in python. It deletes an object with del x.

For example:

>>> x = 5
>>> x
5
>>> del x
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined