5. Shared Variables

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In-Page Navigation

1. Demo 1: Create a Shared Variable
2. Demo 2: Change the Variable
3. It’s Now Your Turn!
   1. Task 1: Increase the score by 10 when the friend fish arrives at the chest
   2. Task 2: Continuously reduce the score when the enemy is at the chest
   3. Task 3: Make the enemy moves faster when the score is higher

This tutorial requires PyScratch version 2.1.0 or above.

Demo 1: Create a Shared Variable

Let’s add a score for this game by creating a shared variable.

This can be done by putting the value in this dictionary-like object pyscratch.game. In this example, we put these lines in the beginning of main.py, but you can put them anywhere in any file.

main.py

import pyscratch as pysc
from pyscratch import game

game['score'] = 0
score_display = pysc.create_shared_data_display_sprite('score') 
# note that the score display is also a sprite and you can control it if you want. 
# for example, to make it draggable: 
score_display.set_draggable(True)

This is similar to creating a variable in Scratch under the variable tab with the display enabled.

Without variable display, only one line is necessary.

import pyscratch as pysc
from pyscratch import game

game['score'] = 0

Note

The shared variable should always be created outside the event.

Demo 2: Change the Variable

Let’s increase the score by one when the enemy is clicked.

enemy.py

# make sure this line exists on the top of the script
from pyscratch import game

@enemy.when_this_sprite_clicked()
def clicked():
    """
    change the enemy location with a fade out effect and increment the score
    """
    game['score'] += 10 # same as the Scratch block "change 'my variable' by 10"
    
    # the logic to make the enemy fade out and reappear
    ...
    

Caveat!

The access of these shared variables are guaranteed only inside the events.

If you try to access (or change) a shared variable from outside the events, you may or may not encounter an error, depending on many arbitrary factors.

It’s Now Your Turn!

Task 1: Increase the score by 10 when the friend fish arrives at the chest

• Increase the score before the friend fish reappears after arriving the chest (the centre of the window)

Task 2: Continuously reduce the score when the enemy is at the chest

• Create a new event, inside a forever loop, check if the enemy is within a certain distance to the centre of the window
• If so, reduce the score by 1.
• Yield for 0.1 second (so the score decreases by 10 for each second the enemy is in the centre)

Task 3: Make the enemy moves faster when the score is higher

• For example, make the speed a constant plus a percentage of the score
  • speed = 5 + game['score']*0.1

The game might look like this

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