Python说在赋值之前提到的变量在嵌套在for循环中时被赋值吗？

Question

EDIT
Well I'm an idiot for deleting the thing I'm looping through. Thanks y'all.

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I've tried looking up answers but honestly this is just boggling me.
I have a for loop which loops through lists in a list, but then in an if statement nested into the for loop it says the thing it is looping with is not defined?

for monster in self.monsters:
    print("google chrome")
    if monster[1][1] <= 0:
        self.exp_gotten += monster[1][8] 
        for j in self.turns:
            if j[0] == monster[1][0]:
                del j
                self.defeated_monsters.append(monster)
                del monster

self.monsters is a list containing other lists for the monsters. The lists are like ["Monster Name", [monster_id, hp, mp, ...]]. Monster[1][1] is the HP stat, and it checks if it is smaller than 0, indicating its been defeated. It then adds the exp, then deletes the monster from the turns list, adds it to the list of defeated monsters, then deletes the monster itself.
Except when it comes to this part, I keep getting "monster variable referenced before assignment"

File "C:\Users\Admin\Documents\Dave's stuff\Python\COURSEWORK\battle.py", line 150, in check_if_fin
    if j[0] == monster[1][0]:
UnboundLocalError: local variable 'monster' referenced before assignment

I just don't get what I'm doing wrong.

Answer 1

Your inner for loop deletes the monster variable:

    for j in self.turns:
        if j[0] == monster[1][0]:
            del j
            self.defeated_monsters.append(monster)
            del monster
            ^^^^^^^^^^^

If self.turns contains more than one element and and anything but the last enters the if block, you'll delete monster and get that error. You probably want to throw in a break statement or otherwise exit the loop if you're done.

It's tricky to remove objects from a list that you're currently iterating over. One solution would be to use intermediate lists:

new_monsters = []

for monster in self.monsters:
    # It's usually clearer to remove unnecessarily nested `if` statements
    if monster[1][1] > 0:
        continue

    self.exp_gotten += monster[1][8] 

    for j in self.turns:
        if j[0] == monster[1][0]:
            self.defeated_monsters.append(monster)

            break  # Don't continue checking, you've already defeated the monster
    else:
        # We never broke out of the above loop, so we never defeated the monster
        new_monsters.append(monster)

self.monsters = new_monsters

Finally, code like monster[1][8] and monster[1][1] is really difficult to manage. Consider setting up your monster as a class with descriptive attributes or at the very least a namedtuple . That way, you can use monster.exp instead of monster[1][8] .