1. Guide to Programming with Python
Week13
Chapter Ten
GUI Development: The Mad Lib Program

2. 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

3. 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

4. The Mad Lib Program
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5. Buttons’ on Strike (I) (II) (III) (IV) from 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 = Button(app, text = "I am button #3")
button3.grid()
button3['text'] = "I am button #3”
root.mainloop() #must start up the window's event loop!!!
(I)
(II)
(III)
(IV)

6. (I) Creating a Root Window
from 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

7. (II) Creating a Frame Master: A widget that contains other widgets
app = 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
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8. (III) Using Widgets Widget: GUI elements (short for "window gadget")
button1 = Button(app, text = "I am button #1")
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
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9. (VI) Entering a Root Window’s Event Loop
root.mainloop()
Root window's event loop entered
Window stays open, waiting to handle events
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10. Widgets 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”)

11. Creating a GUI Using a Class
Organizing code into classes can make programming easier
Often beneficial to write larger GUI programs in OOP style
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12. Defining the Application Class
class 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)

13. 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

14. 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
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15. 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
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16. Buttons That Do Something
class 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 = Button(self) self.button3.configure(text = "Button #3 resets") self.button3["command"] = self.clear_count self.button3.grid() def update_count(self): self.bttn_clicks += 1 def clear_count(self): self.bttn_clicks = 0

17. Creating the Event Handler
def 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
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18. Binding the Event Handler
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()
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
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19. The Longevity Program Label Label Entry Button Text
How the widgets are created?
How the widgets are arranged?
How the “Submit” button can do something?

20. Label Label Entry Button Text 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
Button
Text

21. The Movie Chooser Program
Label
Checkbutton
Text
How to create the check buttons and associate them with the event?

22. 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)

23. 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

24. 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
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25. Using Radio Buttons self.favorite = StringVar() 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()
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."

26. 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