Event triggers changing the user interface

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Quick Questions

Shade in the A or B circle for each question.

1. Which line changes the text of a tkinter label called status when a handler runs?

A status.text = config('Saved')

B status.config(text='Saved')

2. What is the main reason a handler calls label.config(text=...)?

A To give the user feedback after an event

B To create a new window each time

3. A button's handler contains this line: msg.config(fg='red'). What happens when the button is clicked?

A The colour of the text in msg changes to red

B The button itself turns red

4. Which handler gives feedback when a key is pressed?

A def on_key(event): label.config(event.keysym)

B def on_key(event): label.config(text=event.keysym)

5. True or false: the label on screen updates by itself when you change a variable, without calling config().

A False. You must call config() in the handler

B True. The label always follows the variable

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1label.config(text='Saved')		Aconfig() needs the option name text= before the value. It should be label.config(text='Done').
2button.config(bg='green')		Bdef on_click(event): label.config(text='Clicked!')
3A key press handler updates a label to show which key the user pressed		CThe text value is missing quotes, so Python treats Done as a variable name and gives a NameError. It should be text='Done'.
4A mouse click handler changes a label so the user knows the click was detected		Ddef on_key(event): label.config(text=event.keysym)
5label.config(text=Done)		EChanges the background colour of a widget when the handler runs
6label.config('Done')		FChanges the text shown on a label so the user sees feedback after an event

Definitions

label.config(text='Done')

Fill in the Blanks

Complete each line of code by filling in the missing parts.

label.______(text='Done')

label.config(____='Saved')

def warn(): label.config(__='red') button = tk.Button(root, command=warn)

def show(event): label.config(text='Key pressed') root.____('<Key>', show)

def show(_____): label.config(text='Mouse clicked') label.bind('<Button-1>', show)

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A def done():

B label.config(txt='Done')

C btn = tk.Button(command=done)

Question 2

A def on_key(event):

B key = event.keysym

C label.text = key

D root.bind('<Key>', on_key)

Question 3

A def hover(event):

B btn.config(bg='yellow')

C msg.config(text='Hover')

D btn.bind('<Enter>', hover())

Question 4

A def leave(event):

B btn.config(bg='white')

C msg.config(text='Bye')

D btn.bind(leave, '<Leave>')

Question 5

A def on_key():

B label.config(text='Key!')

C root.bind('<Key>', on_key)

Answer Key

Event triggers changing the user interface

Section A: Quick Questions

B — status.config(text='Saved')

A — To give the user feedback after an event

A — The colour of the text in msg changes to red

B — def on_key(event): label.config(text=event.keysym)

A — False. You must call config() in the handler

Section B: Match the Pairs

label.config(text='Saved') → Changes the text shown on a label so the user sees feedback after an event

button.config(bg='green') → Changes the background colour of a widget when the handler runs

A key press handler updates a label to show which key the user pressed → def on_key(event): label.config(text=event.keysym)

A mouse click handler changes a label so the user knows the click was detected → def on_click(event): label.config(text='Clicked!')

label.config(text=Done) → The text value is missing quotes, so Python treats Done as a variable name and gives a NameError. It should be text='Done'.

label.config('Done') → config() needs the option name text= before the value. It should be label.config(text='Done').

Section C: Definitions

label.config(text='Done') — A handler runs when an event happens and can call config() to change the interface, such as updating a label's text to give the user feedback.

Section D: Fill in the Blanks

label.config(text='Done')

label.config(text='Saved')

def warn():
    label.config(fg='red')
button = tk.Button(root, command=warn)

def show(event):
    label.config(text='Key pressed')
root.bind('<Key>', show)

def show(event):
    label.config(text='Mouse clicked')
label.bind('<Button-1>', show)

Section E: Spot the Error

B — The option that sets a label's text is text, not txt. It should be label.config(text='Done'), otherwise tkinter raises an error and the label never updates.

C — Setting an attribute called text does not change what the label shows on screen. Use label.config(text=key) so the handler updates the interface.

D — hover() calls the handler straight away instead of passing it to bind. It should be btn.bind('<Enter>', hover) so it only runs when the mouse enters the button.

D — The arguments to bind are in the wrong order. The event name comes first, then the handler: btn.bind('<Leave>', leave).

A — bind() passes an event object to the handler, so the handler needs a parameter. It should be def on_key(event):.