Karel (now in Python)

Karel is a pretty snazzy environment for learning to program. You can read about it here.
I decided to write a Karel environment for Python, after seeing that all of the others had too many dependencies for beginners.

Stephen Altamirano (alts/karel)

Write simple Karel programs

Writing in Python is super fast and easy! Save a text file YOUR_PROGRAM.py in this folder, use import and start coding!

from karel_run import *
# Simple program
move()
turn_left()
move()

For a true unix executable, add the shebang, then the right to execute with chmod +x YOUR_PROGRAM.py and run it as ./YOUR_PROGRAM.py.

Karel functions

These are the functions you can use to command Karel after importing from karel_run:

from karel_run import *
# Movement
move()       # Karel moves in the direction he is facing
turn_left()  # Karel turns left
turn_right() # Karel turns right
# Beepers
pick_beeper() # Karel tries to pick up a beeper
put_beeper()  # Karel puts down a beeper (if he has any)
beeper_is_present() # True if Karel stands on a beeper
# Walls
front_is_blocked()  # True if Karel can't move forward
front_is_treasure() # True if Karel is standing in front of a Treasure
# Direction
facing_north()  # True if Karel is facing north (^)
facing_south()  #                         south (v)
facing_east()   #                          east (>)
facing_west()   #                          west (<)
# Settings and execution
set_speed(100)   # How fast Karel moves, 0 to 100
set_karel_beepers(None)  # Set Karel's beepers, with None working as inf.
pause()      # Pause execution, press any key to continue
exit()       # End execution

Note that the map is loaded and screen started in the moment of from karel_run import *. If you only need raw objects and methods see karel.py.

Karel world

Karel maps are also simple text files and look like this one:

1..#...
#....^.

Karel is represented by the arrow (^) looking up. There are two walls (#) and one beeper in the upper left corner (1). There is no treasure ($).

Planing to write maps? Check out the vim highlighting! :)

Run your program

Open the terminal and write this command:

python3 YOUR_PROGRAM.py YOUR_MAP.karelmap

Press Q to quit or P to pause program. Program pauses when Karel tries to make an illegal move.

Try out your map with interactive

Use the command:

python3 karel_run.py YOUR_MAP.karelmap

You can now use your keyboard to control Karel.

⬆ ... move()
⬅ ... turn_left()
⮕ ... turn_right()
I  ... pick_beeper()
U  ... put_beeper()
Q  ... stop()

Examples

You can try these examples or study them for great knowledge. You can always quit their execution with Q.

Example treasure

Run the program example.py (also below) with worlds 00 - 03_window. Karel will walk to the wall and then search for a treasure in the walls.

  

The idea comes from a paper on cooperative learning in CS1.

Karel searching for treasure Python code

from karel_run import *

while not front_is_blocked():
    move()

while not front_is_treasure():
    turn_left()
    if front_is_blocked():
        turn_left()
    # FIX: add else
    move()
    turn_right()

Langton's ant

The program langton.py (also below) makes Karel a Langton's ant, using a single beeper to mark a tile as "Black" and Karel can pick it up to make it "White".

The ant moves seemingly randomly, but makes a nice picture in about 11000 steps. Try with the world 04_140x50.

Langton's ant Python code

from karel_run import *
set_speed(100)

while True:
    if not beeper_is_present():  # At a white square
        put_beeper()  # flip the color of the square
        turn_right()  # turn 90° right
        move()        # move forward one unit
    else:  # At a black square
        pick_beeper() # flip the color of the square
        turn_left()   # turn 90° left
        move()        # move forward one unit