Guide to Programming with Python Chapter Ten GUI Development: The Mad Lib Program.

Guide to Programming with Python

Chapter TenGUI Development: The Mad Lib Program

Objectives Events-driven programming! Work with a GUI toolkit

– Create and fill frames– Create and use widgets

• Buttons

• text entries

• text boxes

• check buttons

• radio buttons

– Layout of the widget– Create event handlers and bind (associate) events

with event handlers

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Understanding Event-Driven Programming

Event-driven program: A program that responds to actions regardless of the order in which they occur (vs structured programming)

Event: Something that happens involving a program's objects (mouse moves over; click of a button, etc)

Event handler: Code that runs when a specific event occurs

Bind: To associate an event with an event handler Event loop: A loop that checks for events and calls

appropriate event handlers when they occur GUI programs traditionally event-driven: the users

control the flow of the program

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The Mad Lib Program

Guide to Programming with Python 4

Buttons’ on Strikefrom Tkinter import *root = Tk() #a root window, upon which other GUI elements can be added

root.title("Simple GUI Demo") #add title

root.geometry("400x200") #change the size of the window

app = Frame(root) #create a frame, upon which other Widgets can be added

app.grid() #need to invoke grid() method

button1 = Button(app, text = "I am button #1")

button1.grid()

button2 = Button(app)

button2.grid()

button2.configure(text = "I am button #2”)


button3.grid()

button3['text'] = "I am button #3”

root.mainloop() #must start up the window's event loop!!!

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(I)

(II)

(III)

(IV)

(I) Creating a Root Windowfrom Tkinter import *

root = Tk()

root.title("Simple GUI")

root.geometry("200x100”) # takes a string

To create a root window, instantiate object of the Tkinter class Tk– Tkinter is a GUI module

– Imports all Tkinter into global scope

– Normally, avoid this kind of import *

– Some modules designed to be imported this way

– Saves typing and makes for cleaner code (no need to prefix the module name)

Modify a window’s appearance by changing title and geometry

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(II) Creating a Frameapp = Frame(root)

app.grid()

Master: A widget that contains other widgets Layout Manager: Controls arrangement of widgets Frame is widget that can hold other widgets When creating widget, must pass its master to

constructor of new object Here, root is master that contains app grid()

– Method that all widgets have– Associated with grid layout manager


(III) Using Widgets


button1.grid()

Widget: GUI elements (short for "window gadget") Button widget

– Is a button in GUI– Can be activated by user to perform some action

Button Class– For a button widget– Master is first argument passed to constructor– text parameter for widget's text – grid() method invoked ensures widget visible


(VI) Entering a Root Window’s Event Loop

root.mainloop()

Root window's event loop entered Window stays open, waiting to handle events


Widgets

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Widgets Description Example

Label Uneditable text or icon Label(root, text=“I am a label”)

Button A button that can be activated by the user to perform some action

Button(root, text = “Go”)

Text Allow user to input multiple lines

Text(root, width=35,height=5,wrap=WORD)

Entry Good for a line Entry(root)

Check button

Allow user to select choices from a group

Checkbutton(root, text=“Comedy”)

Radio button

Radio buttons only allow one button in a group to be selected at once

Radiobutton(root, text=“Comedy”)

Creating a GUI Using a Class

Organizing code into classes can make programming easier

Often beneficial to write larger GUI programs in OOP style


Defining the Application Classclass Application(Frame):

def __init__(self, master):

# create a frame (need to get master 'root’)

Frame.__init__(self, master)

self.grid()

self.CreateWidgets()

def CreateWidgets(self):

# create button #1

self.button1 = Button(self, text = "I am button #1”)

self.button1.grid()

…

def main():

root = Tk()

root.title("Simple GUI Demo")

root.geometry("400x200”)

app = Application(root)

root.mainloop()

main()

# Application object is just specialized type of Frame object (derived from Frame)

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Placing a Widget with the Grid Layout Manager

Grid layout manager lets you place widgets at specific locations by treating frame as a grid of cells at row and column numbers

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Widgets Have grid() Method def create_widgets(self):

self.inst_lbl = Label(self, text = "Enter

password for the secret of longevity")

self.inst_lbl.grid(row = 0, column = 0,

columnspan = 2, sticky = W)

grid() method– row takes integer, defines row object placed in master – column takes integer, defines column object placed in

master– columnspan takes integer, defines width in columns– sticky takes constants (including N, S, E, W), positions

widget within cell


Binding Widgets and Event Handlers

So far, GUI programs haven't had event handlers Widgets are like light fixtures without electrical

wiring Write event handlers and bind them with events


Buttons That Do Somethingclass Application(Frame):

def __init__(self, master):

...

self.bttn_clicks = 0 #initialize the button_clicks

self.create_widgets()

def create_widgets(self):

self.button1 = Button(self, text = "Button #1 does nothing")

self.button1.grid()

self.button2 = Button(self)

self.button2["text"] = "Button #2 counts: clicks=" + str(self.bttn_clicks)

self.button2["command"] = self.update_count

self.button2.grid()


self.button3.configure(text = "Button #3 resets")

self.button3["command"] = self.clear_count

self.button3.grid()

def update_count(self):

self.bttn_clicks += 1

self.button2["text"] = "Button #2 counts: clicks=" + str(self.bttn_clicks)

def clear_count(self):

self.bttn_clicks = 0

self.button2["text"] = "Button #2 counts: clicks=" + str(self.bttn_clicks) 16

Creating the Event Handlerdef update_count(self):

self.bttn_clicks += 1

self.button2["text"] = "Button #2 counts: clicks=" +\

str(self.bttn_clicks)

update_count() increments total number of button clicks and changes text to reflect new total


Binding the Event Handler def create_widgets(self):

self.button1 = Button(self, text = "Button #1 does nothing")

self.button1.grid()


self.button2["text"] = "Button #2 counts: clicks=" +\

str(self.bttn_clicks)

self.button2["command"] = self.update_count

self.button2.grid()

Set widget’s command option to bind activation of widget with event handler

command option bound to update_count() method When button clicked, update_count() invoked


The Longevity Program

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Label

Label Entry

Text

Button

How the widgets are created?How the widgets are arranged?How the “Submit” button can do something?

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class Application(Frame): def __init__(self, master): … def create_widgets(self): self.inst_lbl = Label(self, text = "Enter password for the secret of longevity") self.inst_lbl.grid(row = 0, column = 0, columnspan = 2, sticky = W) self.pw_lbl = Label(self, text = "Password: ") self.pw_lbl.grid(row = 1, column = 0, sticky = W) self.pw_ent = Entry(self) self.pw_ent.grid(row = 1, column = 1, sticky = W) self.submit_bttn = Button(self, text = "Submit", command = self.reveal) self.submit_bttn.grid(row = 2, column = 0, sticky = W) self.secret_txt = Text(self, width = 35, height = 5, wrap = WORD) self.secret_txt.grid(row = 3, column = 0, columnspan = 2, sticky = W) def reveal(self): contents = self.pw_ent.get() if contents == "secret": #get the message here self.secret_txt.delete(0.0, END) self.secret_txt.insert(0.0, message)

Label

Label

Entry

Text

Button

The Movie Chooser Program

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Label

Checkbutton

Text

How to create the check buttons and associate them with the event?

class Application(Frame): def __init__(self, master): … def create_widgets(self): … self.likes_comedy = BooleanVar() Checkbutton(self, text = "Comedy", variable = self.likes_comedy, command = self.update_text ).grid(row = 2, column = 0, sticky = W) … self.results_txt = Text(self, width = 40, height = 5, wrap = WORD) self.results_txt.grid(row = 5, column = 0, columnspan = 3)

def update_text(self): #get the message, likes if self.likes_comedy.get(): likes += "You like comedic movies.\n” …. self.results_txt.delete(0.0, END) self.results_txt.insert(0.0, likes)

Using Check Buttons self.likes_comedy = BooleanVar()

Checkbutton(self,

text = "Comedy",

variable = self.likes_comedy,

command = self.update_text

).grid(row = 2, column = 0, sticky = W)

...

if self.likes_comedy.get():

likes += "You like comedic movies.\n”

variable takes BooleanVar for status of check button BooleanVar

– Special class from Tkinter module

– Can reflect check button’s status (Can’t access the value directly; Must invoke object’s get() method

command takes function or method to call when check button is checked or unchecked

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Using Radio Buttons Radio buttons allow user to select one from a

group of choices


Radio buttons (instead of check buttons)

The Movie Chooser 2 Program

Using Radio Buttons

StringVar – Special class from Tkinter module; required by Radiobutton objects– Can reflect status of a group of radio buttons

variable parameter gets StringVar self.favorite The same StringVar object passed to all the radio buttons of the

same group When radio button is selected, StringVar assigned string

referenced by object’s value option– When Comedy radio button selected, self.favorite gets "comedy."

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self.favorite = StringVar() Radiobutton(self, text = "Comedy", variable = self.favorite, value = "comedy.", command = self.update_text ).grid(row = 2, column = 0, sticky = W) ...

message += self.favorite.get()

Summary

A GUI is a graphical user interface A widget, short for window gadget, is a GUI

element A master widget (frame) contains other widgets A layout manager controls the arrangement of

widgets (grid()) An event-driven program responds to actions

regardless of the order in which they occur An event is something that happens involving a

program’s objects, and needs to be associated with event handlers


Guide to Programming with Python Chapter Ten GUI Development: The Mad Lib Program.

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