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Reindeer tender-adventurer


i was trying out reindeer tender when it started giving me this error message

Error Message

Fix Your Code
Try self.pos
Line 14: Cannot read property ‘pos’ of undefined

# This array contains the positions of the pens that we want to put the reindeer in.
penPositions = [ {"x":20,"y":24}, {"x":28,"y":24}, {"x":36,"y":24}, {"x":44,"y":24}, {"x":52,"y":24} ]
# This array is used to track which reindeer have been asssigned to which pen.
assignments = [ None, None, None, None, None, ]
# And this array contains our reindeer.
friends = hero.findFriends()

# Figure out which reindeer are already in their pens.
for deerIndex in range(len(friends)):
    reindeer = friends[deerIndex]
    # Go through each position and see if it matches the reindeer's position.
    for posIndex in range(len(penPositions)):
        penPos = penPositions[posIndex]
        if penPos.x == reindeer.pos.x and penPos.y == reindeer.pos.y:
            # Put the reindeer in the assignments array in slot posIndex.
            assignments[posIndex] = reindeer
            # Remove the reindeer from the friends array.
            # break out of the inner loop here to avoid confusion.

# Assign the remaining reindeer to new positions.
for deerIndex in range(len(friends)):
    # If the reindeer in this array slot is null, skip this and continue to the next one.
    if not reindeer:
    # Look for the first pen with nothing already assigned to it.
    for posIndex in range(len(penPositions)):
        # If there's nothing in this slot of the assignments array, then the pen is open.
        if not assignments[posIndex]:
            # Put the reindeer in the assignments array.
            assignments[posIndex] = reindeer
            # Command the reindeer to move to the pen position.
            hero.command(reindeer, "move", penPositions[posIndex])
            # break out of the inner for loop here so we don't reassign the deer.


the weird thing is that if i replaced reindeer.pos.x with self.pos.x it didn’t have a problem with ```reindeer.pos.y


From the error message and what you said I am guessing that you are over itereating. self.say(reindeer) every loop to make sure what are looking for exists.

I am not sure how the complier handles this bit of code where you change the length of the array you are using to interate, but I am guessing that is where the problem is. It would also explain why using self.pos.x would make it work (becuase the code would never run)

friends = self.findFriends
for i in range(len(friends))
  if condition:


then why does it not have a problem with reindeer.pos.y?


Because pen.pos.x is self.pos.x will never evaluate as true.
Python stops evaluating an if statement the moment it cannot be true. Thus you can do things like this:
if enemy and self.distanceTo(enemy) < 10
as the code stops with if enemy.

You may be able to fix your code by checking for reindeer first on line 14:
if reindeer and penPos.x is reindeer.pos.x and penPos.y is reindeer.pos.y:
It’s a lazy fix, but it may work or not depending on what the problem is, which is why it is a good idea to self.say(things) when you have errors. It helps isolate the problem so you can work on a solution.


Maybe there’s a way to “remove” friends without changing the size of the friends array? The comment there could probably be phrased better.