20130729 Simple Calculator.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
#  20130729 Simple Calculator.py
#

# imports
from gi.repository import Gtk

# constants
XML_FILE = "calculator.glade"
MAIN_WINDOW_NAME = "Main_window"
INPUT_A_NAME = "InputA_entry"
INPUT_B_NAME = "InputB_entry"
RESULT_NAME = "Result_entry"

# class to handle signals coming from the GTK window
class Signal_Handler:
    def on_Main_window_delete_event(self, *args):
        Gtk.main_quit(*args)

    def on_Add_button_released(self, button):
# get inputs
        input_a, input_b, input_valid = get_inputs()
# set the result
        if input_valid:
            set_result(input_a + input_b)
        else:
            set_result("Invalid input(s).")
# end on_Add_button_released(self, button)

    def on_Subtract_button_released(self, button):
# get inputs
        input_a, input_b, input_valid = get_inputs()
# set the result
        if input_valid:
            set_result(input_a - input_b)
        else:
            set_result("Invalid input(s).")
# end on_Subtract_button_released(self, button)

    def on_Multiply_button_released(self, button):
# get inputs
        input_a, input_b, input_valid = get_inputs()
# set the result
        if input_valid:
            set_result(input_a * input_b)
        else:
            set_result("Invalid input(s).")
# end on_Multiply_button_released(self, button)

    def on_Divide_button_released(self, button):
# get inputs
        input_a, input_b, input_valid = get_inputs()
# set the result
        if input_valid:
            if (input_b != 0.0):
                set_result(input_a / input_b)
            else:
                set_result("Cannot divide by zero.")
        else:
            set_result("Invalid input(s).")
# end on_Divide_button_released(self, button)

    def on_ANS_A_button_released(self, button):
        copy_result(RESULT_NAME, INPUT_A_NAME)
# end on_ANS_A_button_released(self, button)

    def on_ANS_B_button_released(self, button):
        copy_result(RESULT_NAME, INPUT_B_NAME)
# end on_ANS_B_button_released(self, button)
# end Signal_Handler class

# creates the main window.
def create_window():
# declare builder globally so it can be used elsewhere
    global builder
    builder = Gtk.Builder()
# point the builder to the XML file describing the layout
    builder.add_from_file(XML_FILE)
# connect the builder to the signal handler
    builder.connect_signals(Signal_Handler())
# get the window object
    window = builder.get_object(MAIN_WINDOW_NAME)
# show the window
    window.show_all()
# end create_window()

def get_inputs():
    input_valid = True
# get input A
    input_a_object = builder.get_object(INPUT_A_NAME)
# check if a number has been entered
    if is_a_float(input_a_object.get_text()):
# if it has
        input_a = float(input_a_object.get_text())
    else:
# if not
        input_a = 0.0
        input_a_object.set_text("Enter a number.")
        input_valid = False
# get input B
    input_b_object = builder.get_object(INPUT_B_NAME)
# check if a number has been entered
    if is_a_float(input_b_object.get_text()):
# if it has
        input_b = float(input_b_object.get_text())
    else:
# if not
        input_b = 0.0
        input_b_object.set_text("Enter a number.")
        input_valid = False
# return inputs
    return input_a, input_b, input_valid
# end get_inputs()

def is_a_float(input):
# try to convert the input to a float.
# if you can't then it's likely not a number
    try:
        float(input)
        return True
    except ValueError:
        return False
# end is_a_float(input)

def set_result(result):
# output result
    builder.get_object(RESULT_NAME).set_text(str(result))
# end set_result(result)

def copy_result(result_name, input_name):
# copy result to an input
    result_object = builder.get_object(result_name)
    input_object = builder.get_object(input_name)
    if is_a_float(result_object.get_text()):
        input_object.set_text(result_object.get_text())
# end copy_result(result_name, input_name)

# main function
def main():
    create_window()
    Gtk.main()
    return 0
# end main()

if __name__ == '__main__':
    main()