I tried solving “Polygonception” from the Glacier using the technique shown in previous levels, but for some reason I keep getting the error above.

Here’s what I’m doing:

```
startOffset = Vector(-15, -15)
endOffset = Vector(15, -15)
enemies = self.findEnemies()
for enemy in enemies:
start = Vector.add(enemy.pos, startOffset)
end = Vector.add(enemy.pos, endOffset)
sides = enemy.sides
polygon(start, end, sides)
```

where polygon is defined as follows:

```
def polygon(start, end, side):
full = Vector.subtract(end, start)
......................
```

At the very first line of polygon the error appers. What am I doing wrong?