Convert expression to a postfix notation with GTK+ GUI

postfix_converter_graphical.py

from gi.repository import Gtk

class MainWindow(Gtk.Window):

    def __init__(self):
        Gtk.Window.__init__(self, title="Postfix")
        self.set_border_width(10)
        self.set_size_request(250, 150)

        # Layout
        vbox = Gtk.Box(orientation=Gtk.Orientation.VERTICAL, spacing=8)
        self.add(vbox)

        # Label
        self.label = Gtk.Label()
        self.label.set_label('Postfiksni izraz')
        vbox.pack_start(self.label, True, True, 0)

        # Input
        self.input = Gtk.Entry()
        self.input.set_text('a + b * c')
        vbox.pack_start(self.input, True, True, 0)

        # Button
        self.button = Gtk.Button(label='Convert to postfix')
        self.button.connect('clicked', self.convert)
        vbox.pack_start(self.button, True, True, 0)

    def convert(self, widget):
        operators = {'(': 0, ')': 0, '+': 1, '-': 1, '*': 2, '/': 2, '%': 2}
        stack = []
        postfix = []

        expression = self.input.get_text().split()

        for ch in expression:
            if ch in operators:
                if ch is ')':
                    while stack and stack[-1] is not '(':
                        postfix.append(stack.pop())
                    stack.pop()
                    continue
                # if stack and operators[ch] <= operators[stack[-1]]:
                if stack and operators[stack[-1]] is 2 and (operators[ch] is 2 or operators[ch] is 1):
                    postfix.append(stack.pop())
                stack.append(ch)
            else:
                postfix.append(ch)

        for _ in range(len(stack)):
            postfix.append(stack.pop())

        output = ' '.join(str(e) for e in postfix)
        self.label.set_label(output)



window = MainWindow()
window.connect("delete-event", Gtk.main_quit)
window.show_all()
Gtk.main()

Should be updated to support powers (x^y).
You can try to add it, as well as other additional features. 😄