<br>for this code m getting this error :<br><br>CODE : <br>def ComputeClasses(data):<br>    radius = .5 <br>    points = []<br>    for cy in xrange(0, data.height):<br>        for cx in xrange(0, data.width):<br>            if data[cy,cx] != (0.0,0.0,0.0):<br>
                centre = data[cy, cx]<br>                points.append(centre)    <br>                <br><br>            change = True<br><br>            while change:<br>                <br>                for ring_number in xrange(1, 1000):<br>
                    change = False<br>                    new_indices = GenerateRing(cx, cy, ring_number)<br>           <br><br>                    for idx in new_indices:<br>                        point = data[idx[0], idx[1]]<br>
                   <br>                        if point == (0.0, 0.0, 0.0 ):<br>                          continue<br>                        else:<br>                            dist = distance(centre, point)<br>                            if  dist < radius :<br>
                                print point <br>                                points.append(point)<br>                                change = True<br>                                print change<br>                  <br>
                <br>            break <br><br><br>ERROR : <br>Traceback (most recent call last):<br>  File "Z:\modules\classification2.py", line 74, in <module><br>    ComputeClasses(data)<br>  File "Z:\modules\classification2.py", line 56, in ComputeClasses<br>
    dist = distance(centre, point)<br>UnboundLocalError: local variable 'centre' referenced before assignment<br><br>And i am unable to understand .. WHY ?<br><br><br>