Python Simple Tkinter Calculator Part 3 (Build methods and bind buttons)

Simple Tkinter Calculator Part 3
In part3 we will:

• Create methods in our Controller class
• Bind the buttons to the methods
• Create a simple validation

Create methods

    def valid_input(self,arg):
        ''' Method for validating input '''
        if arg.isalpha() or arg == '=':
            return False
        else:
            return True
 
    def clear(self, event):
        ''' Method for clearing the entry field '''
        self.window.entry.delete(0, 'end')

    def insert(self, var):
        ''' Method for inserting numbers in the entry field '''
        self.window.entry.insert('end', var)

    def calculate(self, event):
        ''' Method for doing calculations '''

        # Get the values of the entry field
        values = self.window.entry.get()

        # Do and get the calculations from the entry field using eval
        # It is reccommended not to use eval but, for our purpose
        # it will be fine
        result = eval(values)

        # Checking if our number is a float and is a whole number.
        # If it is a whole number it will remove the .0
        # else return the number as is
        if isinstance(result, float):
            result = Decimal(result).normalize()
        else:
            result = result

        # Clear the entry field and insert the calculation back into the entry field
        self.window.entry.delete(0, 'end')
        self.window.entry.insert('end', result)

Create the button commands, binds and validation

        # Create commands for our buttons
        for btn in self.window.btns:
            # If the buttons are not = or clear - give the insert command
            if btn['text'] not in ['Clear', '=']:
                btn['command'] = lambda var=btn['text']: self.insert(var)
            elif btn['text'] == 'Clear':
                # If the button is the clear button - clear the field
                btn['command'] = lambda: self.clear(None)
            else:
                # Else calculate
                btn['command'] = lambda var=btn['text']: self.calculate(var)

        # Bind keys to perform some actions
        self.window.parent.bind('<Return>', lambda var=btn['text']: self.calculate(var))
        self.window.parent.bind('<KP_Enter>', lambda var=btn['text']: self.calculate(var))
        self.window.parent.bind('<Escape>', self.clear)

        # Validate input - Needs to be numbers or *,+,/,-
        valid = self.window.parent.register(self.valid_input)
        self.window.entry.configure(validate='key', validatecommand=(valid, '%S'))