Responding to keyboard events

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Quick Questions

Shade in the A or B circle for each question.

1. Which line makes tkinter call on_key every time any key is pressed?

A root.bind('<KeyPress>', on_key)

B root.bind('<KeyPress>', on_key())

2. A handler for a key press needs which parameter?

A def on_key(event):

B def on_key():

3. Which expression tells you the name of the key that was pressed?

A root.keysym

B event.keysym

4. A player presses the Up arrow key. What is event.keysym?

A 'Arrow'

B 'Up'

5. Which condition checks that the Escape key was pressed inside the handler?

A if event.keysym == 'Escape':

B if event.keysym = 'Escape':

Match the Pairs

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

Left column		Right column
1root.bind('<KeyPress>', on_key)		AThe handler has no event parameter, so event is undefined and tkinter cannot pass the key press in. It should be def on_key(event):
2event.keysym		BTells tkinter to call the function on_key every time any key is pressed in the window
3A handler function must have a parameter to receive the event that tkinter passes in		Cdef on_key(event):
4Respond only when a specific key, such as the Up arrow, is pressed		DThe handler is called with brackets, so it runs straight away instead of waiting for a key press. Pass on_key without ().
5root.bind('<KeyPress>', on_key())		EGives the name of the key that was pressed, such as 'a', 'Up' or 'space'
6def on_key(): print(event.keysym)		Fif event.keysym == 'Up':

Definitions

root.bind('<KeyPress>', handler)

Fill in the Blanks

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

root.____('<KeyPress>', handler)

def handler(_____): print(event.keysym)

key = event.______

if event.keysym __ 'Up': print('Up arrow')

def press(event): print(event.keysym) root.bind('<KeyPress>', _____)

Spot the Error

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

Question 1

A def key(event)

B print(event.keysym)

C root.bind('<KeyPress>', key)

Question 2

A import tkinter as tk

B root = tk.tk()

C def key(event):

D print(event.keysym)

E root.bind('<KeyPress>', key)

Question 3

A root = tk.Tk()

B def key(event):

C print(event.keysym)

D root.bind('<KeyPress>', key())

E root.mainloop()

Question 4

A def key(event):

B if event.keysym == 'Up':

C print('Moving up'

D root.bind('<KeyPress>', key)

Question 5

A def key(event):

B pressed = event.keysym

C if pressed = 'space':

D print('Jump!')

E root.bind('<KeyPress>', key)

Answer Key

Responding to keyboard events

Section A: Quick Questions

A — root.bind('<KeyPress>', on_key)

A — def on_key(event):

B — event.keysym

B — 'Up'

A — if event.keysym == 'Escape':

Section B: Match the Pairs

root.bind('<KeyPress>', on_key) → Tells tkinter to call the function on_key every time any key is pressed in the window

event.keysym → Gives the name of the key that was pressed, such as 'a', 'Up' or 'space'

A handler function must have a parameter to receive the event that tkinter passes in → def on_key(event):

Respond only when a specific key, such as the Up arrow, is pressed → if event.keysym == 'Up':

root.bind('<KeyPress>', on_key()) → The handler is called with brackets, so it runs straight away instead of waiting for a key press. Pass on_key without ().

def on_key(): print(event.keysym) → The handler has no event parameter, so event is undefined and tkinter cannot pass the key press in. It should be def on_key(event):

Section C: Definitions

root.bind('<KeyPress>', handler) — Links a key press to a handler function. Each time a key is pressed, tkinter calls handler(event), and event.keysym tells you which key it was.

Section D: Fill in the Blanks

root.bind('<KeyPress>', handler)

def handler(event):
    print(event.keysym)

key = event.keysym

if event.keysym == 'Up':
    print('Up arrow')

def press(event):
    print(event.keysym)
root.bind('<KeyPress>', press)

Section E: Spot the Error

A — A function header must end with a colon. The first line should be def key(event): so the handler body can follow.

B — Python is case sensitive. The window class is Tk with a capital T, so it must be root = tk.Tk(). Without it, root.bind() has no window to work on.

D — bind() needs the handler function itself, not the result of calling it. Writing key() runs it straight away. It should be root.bind('<KeyPress>', key).

C — The print call is missing its closing bracket, which causes a SyntaxError. It should be print('Moving up').

C — A single = assigns a value, but an if condition needs the comparison operator ==. It should be if pressed == 'space':.