1. Python Slots Conflicts With Class Variables
2. Python Class Variables Access
3. Python Class Member Variable

Traditional syntax: SIGNAL and SLOT QtCore.SIGNAL and QtCore.SLOT macros allow Python to interface with Qt signal and slot delivery mechanisms. This is the old way of using signals and slots. The example below uses the well known clicked signal from a QPushButton.The connect method has a non python-friendly syntax. Instead of changing a class variable Python creates a new instance variable with the same name. Hence, the instance variables have precedence over class variables when searching for an attribute value. Mutable class variables. You need to be very careful when working with mutable class variables (e.g., list, set, dictionary). Very simple and intuitive. For more information on Python decorators, you might want to checkout the article - Python Decorators Overview to familiarise yourself. Finally, let's instantiate a Circle, hook up the signals to the slots, and move and resize it.

The ‘not’ is a Logical operator in Python that will return True if the expression is False. The ‘not’ operator is used in the if statements.

For example:

if not x

If x is True, then not will evaluate as false, otherwise, True.

Other logical operators:The and operator OR operator

I will show you a few examples to make things clearer regarding how to use the not operator in the coming section.

Python not operator example with if statement

In the following example, a variable x is assigned a value 10. The ‘not’ is used in the if statement as follows:

if not x > 10:

See the code and result.

See online demo and code

As x>10 is False, so not operator evaluated as True, thus the if statement is True and code inside the if statement executed. See next example that will make things even clearer.

How not operator works?

In this demo, the x is used as follows with not operator:

if not x:

See online demo and code

Python Slots Conflicts With Class Variables

Python Class Variables Access

The expression not x means if x is True or False. In Python, if a variable is a numeric zero or empty, or a None object then it is considered as False, otherwise True. In that case, as x = 10 so it is True. As x is True, so not operator evaluated as False and else part executed. See the same example below where the value of x = 0.

See online demo and code

Python Class Member Variable

A Python not with ‘in’ example

In this example, I will show you how to use the ‘not’ operator with ‘in’. For that, a numeric list of six items is created. This is followed by using a for loop to iterate through the list elements and display their values.

After that, an if statement is used to omit certain numbers to be displayed. There, the not operator is used with the ‘in’ as follows:

See online demo and code

You see, the items that evaluated False as using ‘not’ did not display.

Related Tutorials: