diff --git a/webpython/Dockerfile b/webpython/Dockerfile
index 54f1b014..76eae9dc 100644
--- a/webpython/Dockerfile
+++ b/webpython/Dockerfile
@@ -2,9 +2,10 @@ FROM ubuntu:14.04
 MAINTAINER "Martin v. Löwis"
 RUN locale-gen en_US.UTF-8
 ENV LANG en_US.UTF-8
+ADD assess.py /usr/lib/python3.4/assess.py
 ADD webpython.py /usr/lib/python3.4/webpython.py
 RUN rm /usr/lib/python3.4/turtle.py
 ADD turtle.py /usr/lib/python3.4/turtle.py
 RUN adduser --disabled-password --gecos Python python
 USER python
-WORKDIR /home/python
+WORKDIR /usr/lib/python3.4
diff --git a/webpython/assess.py b/webpython/assess.py
new file mode 100644
index 00000000..b14a13b9
--- /dev/null
+++ b/webpython/assess.py
@@ -0,0 +1,234 @@
+import webpython, contextlib, io, json, sys, turtle, ast
+from webpython import shell
+
+turtle_operations = []
+bindings = {}
+
+class RecordingPen:
+    _pen = None
+    _screen = None
+    def __init__(self):
+        self.operations = turtle_operations
+        self._pos = (0,0)
+        turtle_operations.append(('__init__',()))
+
+    def reset(self):
+        turtle_operations.clear()
+
+    def onclick(self, fun, btn=1, add=None):
+        self.operations.append(('onclick', (fun,)))
+        def eventfun(event):
+            fun(event.x, event.y)
+        bindings['<Button-1>'] = eventfun
+
+    def goto(self, x, y):
+        self._pos = (x,y)
+        self.operations.append(('goto', (x,y)))
+
+    def pos(self):
+        self.operations.append(('pos', ()))
+        return self._pos
+
+    def __getattr__(self, method):
+        def func(*args):
+            self.operations.append((method, args))
+        return func
+
+class FakeCanvas(turtle.WebCanvas):
+    def flushbatch(self):
+        pass
+
+    def get_width(self):
+        return 400
+
+    def get_height(self):
+        return 400
+
+    def delete(self, item):
+        pass
+
+    def css(self, key, value):
+        pass
+
+fake_events = []
+def mainloop():
+    while fake_events:
+        e = turtle.Event(fake_events.pop(0))
+        if e.type in bindings:
+            bindings[e.type](e)
+
+turtle.Turtle = RecordingPen
+turtle.WebCanvas = FakeCanvas
+pen = turtle._getpen()
+turtle.mainloop = mainloop
+
+def filter_operations(name):
+    return [o for o in turtle_operations if o[0] == name]
+
+@contextlib.contextmanager
+def capture():
+    global captured_out
+    import sys
+    oldout,olderr = sys.stdout, sys.stderr
+    try:
+        out=[io.StringIO(), io.StringIO()]
+        captured_out = out
+        sys.stdout,sys.stderr = out
+        yield out
+    finally:
+        sys.stdout,sys.stderr = oldout, olderr
+        out[0] = out[0].getvalue()
+        out[1] = out[1].getvalue()
+
+def get_source():
+    message = json.loads(sys.argv[1])
+    return message['data']
+
+def get_ast():
+    s = get_source()
+    return ast.parse(s, "programm.py", "exec")
+
+def has_bare_except():
+    for node in ast.walk(get_ast()):
+        if isinstance(node, ast.ExceptHandler):
+            if node.type is None:
+                return True
+    return False
+
+def runcaptured(prefix='', tracing=None, variables=None, source=''):
+    #message = json.loads(sys.argv[1])
+    #source = prefix + message['data']
+    with open("programm.py", "w", encoding='utf-8') as f:
+        f.write(source)
+    c = compile(source, "programm.py", 'exec')
+    with capture() as out, trace(tracing):
+        if variables is None:
+            variables = {}
+        exec(c, variables)
+    return source, out[0], out[1], variables
+
+def runfunc(func, *args, tracing=None):
+    with capture() as out, trace(tracing):
+        res = func(*args)
+    return out[0], out[1], res
+
+def passed():
+    msg_in = json.loads(sys.argv[1])
+    msg_out = {'cmd':'passed'}
+    msg_out['lis_outcome_service_url'] = msg_in['lis_outcome_service_url']
+    msg_out['lis_result_sourcedid'] = msg_in['lis_result_sourcedid']
+    webpython.shell.sendpickle(msg_out)
+
+def failed(msg):
+    msg_in = json.loads(sys.argv[1])
+    msg_out = {'cmd':'failed', 'data':'Dein Programm ist leider falsch:\n'+msg}
+    msg_out['lis_outcome_service_url'] = msg_in['lis_outcome_service_url']
+    msg_out['lis_result_sourcedid'] = msg_in['lis_result_sourcedid']
+    webpython.shell.sendpickle(msg_out)
+
+def modified(variables, name, val):
+    if variables.get(name) != val:
+        msg_in = json.loads(sys.argv[1])
+        msg_out = {'cmd':'failed',
+                   'data':('Bitte lösche Deine Zuweisung der Variable %s, '+
+                   'damit wir Dein Programm überprüfen können.') % name}
+        msg_out['lis_outcome_service_url'] = msg_in['lis_outcome_service_url']
+        msg_out['lis_result_sourcedid'] = msg_in['lis_result_sourcedid']
+        webpython.shell.sendpickle(msg_out)
+        return True
+    return False
+
+undefined = object()
+def getvar(variables, name):
+    try:
+        return variables['name']
+    except KeyError:
+        name = name.lower()
+        for k,v in variables.items():
+            if k.lower() == name:
+                return v
+        return undefined
+
+def _match(n1, n2):
+    if n1 == n2:
+        return True
+    if n1 is None or n2 is None:
+        return False
+    return n1.lower() == n2.lower()
+
+class Call:
+    def __init__(self, name, args):
+        self.name = name
+        self.args = args
+        self.calls = []
+        self.current = None
+
+    def findcall(self, f):
+        if _match(self.name, f):
+            return self
+        for c in self.calls:
+            r = c.findcall(f)
+            if r:
+                return r
+        return None
+
+    def calling(self, caller, callee):
+        if _match(self.name, caller):
+            for c in self.calls:
+                if _match(c.name, callee):
+                    return True
+        for c in self.calls:
+            if c.calling(caller, callee):
+                return True
+        return False
+
+    def countcalls(self, caller, callee):
+        calls = 0
+        if _match(self.name, caller):
+            for c in self.calls:
+                if _match(c.name, callee):
+                    calls += 1
+            return calls
+        for c in self.calls:
+            r = c.countcalls(caller, callee)
+            if r > 0:
+                return r
+        return 0
+
+class Tracing(Call):
+    def __init__(self):
+        Call.__init__(self, None, None)
+
+    def trace(self, frame, event, arg):
+        if event == 'call':
+            c = Call(frame.f_code.co_name, frame.f_locals.copy())
+            cur = self
+            while cur.current:
+                cur = cur.current
+            cur.calls.append(c)
+            cur.current = c
+            return self.trace
+        elif event in ('return', 'exception'):
+            cur = self
+            if not cur.current:
+                # XXX return without call? happens when invocation of top function fails
+                return
+            while cur.current.current:
+                cur = cur.current
+            cur.current = None
+
+    def start(self):
+        sys.settrace(self.trace)
+
+    def stop(self):
+        sys.settrace(None)
+
+@contextlib.contextmanager
+def trace(t):
+    try:
+        if t:
+            t.start()
+        yield
+    finally:
+        if t:
+            t.stop()
diff --git a/webpython/webpython.py b/webpython/webpython.py
index 350f3755..b81ac680 100644
--- a/webpython/webpython.py
+++ b/webpython/webpython.py
@@ -4,6 +4,7 @@ import io, select, sys, os, threading, code
 import pickle, struct, builtins, json
 #, ressource
 from queue import Queue
+from argparse import ArgumentParser
 
 # hard limit to 64M
 #try:
@@ -163,12 +164,15 @@ builtins.input = shell.input
 #iothread.start()
 
 if __name__ == '__main__':
-    #script = "print (\"Hello world.\")\n\rmsg = input()\n\rprint(\"Out:\")\n\rprint(msg)"
-    #with open("programm.py", "w", encoding='utf-8') as f:
-    #    f.write(script)
-    with open(os.path.join("/", "workspace", "exercise.py"), "r", encoding='utf-8') as f:
+    parser = ArgumentParser(description='A python interpreter that generates json commands based on the standard I/O streams.')
+    parser.add_argument('-f', '--filename', type=str, required=True, default='exercise.py', help='Python file to be interpreted.')
+    args = parser.parse_args()
+
+    filepath = os.path.join("/", "workspace", args.filename)
+    with open(filepath, "r", encoding='utf-8') as f:
         script = f.read()
-    c = compile(script, "exercise.py", 'exec')
+    c = compile(script, args.filename, 'exec')
     exec(c, {})
+
     # work-around for docker not terminating properly
     shell.sendpickle({'cmd':'exit'})