I'm developing an app in Google App Engine. One of my methods is taking never completing, which makes me think it's caught in an infinite loop. I've stared at it, but can't figure it out.

Disclaimer: I'm using http://code.google.com/p/gaeunitlink text to run my tests. Perhaps it's acting oddly?

This is the problematic function:

def _traverseForwards(course, c_levels):
    ''' Looks forwards in the dependency graph '''
    result = {'nodes': [], 'arcs': []}

    if c_levels == 0:
        return result

    model_arc_tails_with_course = set(_getListArcTailsWithCourse(course))
    q_arc_heads = DependencyArcHead.all()

    for model_arc_head in q_arc_heads:
        for model_arc_tail in model_arc_tails_with_course:
            if model_arc_tail.key() in model_arc_head.tails:
                result['nodes'].append(model_arc_head.sink)
                result['arcs'].append(_makeArc(course, model_arc_head.sink))

                # rec_result = _traverseForwards(model_arc_head.sink, c_levels - 1)

                # _extendResult(result, rec_result)

    return result

Originally, I thought it might be a recursion error, but I commented out the recursion and the problem persists. If this function is called with c_levels = 0, it runs fine.

The models it references:

class Course(db.Model):
    dept_code = db.StringProperty()
    number = db.IntegerProperty()
    title = db.StringProperty()
    raw_pre_reqs = db.StringProperty(multiline=True)
    original_description = db.StringProperty()

    def getPreReqs(self):
        return pickle.loads(str(self.raw_pre_reqs))

    def __repr__(self):
        return "%s %s: %s" % (self.dept_code, self.number, self.title)

class DependencyArcTail(db.Model):
    ''' A list of courses that is a pre-req for something else '''
    courses = db.ListProperty(db.Key)

    def equals(self, arcTail):
        for this_course in self.courses:
            if not (this_course in arcTail.courses):
                return False

        for other_course in arcTail.courses:
            if not (other_course in self.courses):
                return False

        return True

class DependencyArcHead(db.Model):
    ''' Maintains a course, and a list of tails with that course as their sink '''
    sink = db.ReferenceProperty()
    tails = db.ListProperty(db.Key) 

Utility functions it references:

def _makeArc(source, sink):
    return {'source': source, 'sink': sink}

def _getListArcTailsWithCourse(course):
    ''' returns a LIST, not SET 
        there may be duplicate entries
    '''
    q_arc_heads = DependencyArcHead.all()
    result = []
    for arc_head in q_arc_heads:
        for key_arc_tail in arc_head.tails:
            model_arc_tail = db.get(key_arc_tail)
            if course.key() in model_arc_tail.courses:
                result.append(model_arc_tail)

    return result

Am I missing something pretty obvious here, or is GAEUnit acting up?