ad prototype exercise

Author: Kristian Rother

README.md

@@ -31,6 +31,7 @@ Below you find development tools and techniques that help you to write programs
 
 ## Coding Strategies
 
+* [The Prototype](prototype.md)
 * [Coding Strategies](writing_code.md)
 * [Debugging](debugging.md)
 

images/prototype.png

@@ -0,0 +1,57 @@
+
+# The Prototype
+
+Before attempting a more costly clean implementation, you may want to check whether the project is feasible at all.
+You can do such a check by implementing a quick and dirty proof of concept: a **prototype**.
+The goal of a prototype is usually to reduce risks in a project.
+
+A prototype can answer questions like:
+
+* is my programming environment set up properly?
+* can we solve a particular algorithmic problem?
+* does a library do what we need?
+* is the algorithm/library fast enough?
+* what safety/security risks are there?
+* did we understand the customer correctly?
+
+## A Prototype for a Snake game
+
+The following code is a prototype for a Snake game.
+The program is a simple game where you move a symbol around with the `WASD` keys.
+The goal of this prototype is to prove that we can process keyboard input and draw into a terminal. 
+
+:::include prototype.py
+
+
+## Exercise: Run the prototype
+
+#### Step 1
+
+Save the code in :::file prototype.py to a Python module.
+
+#### Step 2
+
+On Windows, you need to install `windows-curses`:
+
+    :::bash
+    pip install windows-curses
+
+#### Step 3
+
+Change to the directory with the `.py` file and execute the code with:
+
+    :::bash
+    python prototype.py
+    
+You should see a screen where you can control the `'O'` with the keys **W, A, S and D**:
+
+![prototype output](images/prototype.png)
+
+
+## Reflection Questions
+
+Discuss the following questions:
+
+* Why do you think is the prototype focused on testing the input/output library?
+* Is it more work to write a cleaner version of the prototype later? Why or why not?
+* Is there any code that you don't understand?

prototype.md

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+"""
+Proof-of-concept: move around in a 2D frame
+"""
+import curses
+
+# WASD keys
+KEY_COMMANDS = {97: "left", 100: "right", 119: "up", 115: "down"}
+
+# prepare the screen
+screen = curses.initscr()
+curses.start_color()
+curses.init_pair(1, curses.COLOR_GREEN, curses.COLOR_BLACK)
+curses.curs_set(0)
+curses.noecho()
+curses.raw()
+screen.keypad(False)
+
+win = curses.newwin(20, 20, 0, 0)
+win.nodelay(True)
+
+
+def game_loop(screen):
+    """called by curses"""
+    x, y = 5, 5
+
+    # draw
+    screen.clear()
+    screen.addch(y, x, "O", curses.color_pair(1))
+    win.refresh()
+    screen.refresh()
+
+    while True:
+
+        # handle moves
+        char = win.getch()
+        direction = KEY_COMMANDS.get(char)
+        if direction == "left":
+            x -= 1
+        elif direction == "right":
+            x += 1
+        elif direction == "up":
+            y -= 1
+        elif direction == "down":
+            y += 1
+        else:
+            continue
+
+        # draw
+        screen.clear()
+        screen.addch(y, x, "O", curses.color_pair(1))
+        win.refresh()
+        screen.refresh()
+
+
+if __name__ == "__main__":
+    curses.wrapper(game_loop)
+    curses.endwin()