# Buggy code
def perform_action(self, user, technique, target=None):
    """Do something with the thing: animated

    :param user:
    :param technique: Not a dict: a Technique or Item
    :param target:

    :returns:
    """
    technique.advance_round()

    result = technique.use(user, target)

    try:
        tools.load_sound(technique.sfx).play()
    except AttributeError:
        pass

    # action is performed, so now use sprites to animate it
    # this value will be None if the target is off screen
    target_sprite = self._monster_sprite_map.get(target, None)

    # slightly delay the monster shake, so technique animation
    # is synchronized with the damage shake motion
    hit_delay = 0
    if user:
        # message = "%s used %s!" % (user.name, technique.name)
        message = trans("combat_used_x", {"user": user.name, "name": technique.name})

        # TODO: a real check or some params to test if should tackle, etc
        if technique in user.moves:
            hit_delay += 0.5
            user_sprite = self._monster_sprite_map[user]
            self.animate_sprite_tackle(user_sprite)

            if target_sprite:
                self.task(
                    partial(self.animate_sprite_take_damage, target_sprite),
                    hit_delay + 0.2,
                )
                self.task(partial(self.blink, target_sprite), hit_delay + 0.6)

            # Track damage
            self._damage_map[target].add(user)

        else:  # assume this was an item used
            if result:
                message += "\n" + trans("item_success")
            else:
                message += "\n" + trans("item_failure")

        self.alert(message)
        self.suppress_phase_change()

    else:
        if result:
            self.suppress_phase_change()
            self.alert(
                trans(
                    "combat_status_damage",
                    {"name": target.name, "status": technique.name},
                )
            )

    if result and target_sprite and hasattr(technique, "images"):
        tech_sprite = self.get_technique_animation(technique)
        tech_sprite.rect.center = target_sprite.rect.center
        self.task(tech_sprite.image.play, hit_delay)
        self.task(partial(self.sprites.add, tech_sprite, layer=50), hit_delay)
        self.task(tech_sprite.kill, 3)


# Traceback (KeyError)
Traceback (most recent call last):
File "./tuxemon.py", line 60, in <module>
main()
File "/tmp/Tuxemon/tuxemon/core/main.py", line 109, in main
control.main()
File "/tmp/Tuxemon/tuxemon/core/control.py", line 512, in main
self.main_loop()
File "/tmp/Tuxemon/tuxemon/core/control.py", line 573, in main_loop
self.update(time_delta)
File "/tmp/Tuxemon/tuxemon/core/control.py", line 203, in update
state.update(dt)
File "/tmp/Tuxemon/tuxemon/core/states/combat/combat.py", line 156, in update
self.update_phase()
File "/tmp/Tuxemon/tuxemon/core/states/combat/combat.py", line 328, in update_phase
self.handle_action_queue()
File "/tmp/Tuxemon/tuxemon/core/states/combat/combat.py", line 338, in handle_action_queue
self.check_party_hp()
File "/tmp/Tuxemon/tuxemon/core/states/combat/combat.py", line 614, in check_party_hp
self.faint_monster(monster)
File "/tmp/Tuxemon/tuxemon/core/states/combat/combat.py", line 581, in faint_monster
awarded_exp = monster.total_experience/monster.level/len(self._damage_map[monster])
KeyError: <core.components.monster.Monster object at 0x7fb24236ddd0>

# Fixed code
def perform_action(self, user, technique, target=None):
    """Do something with the thing: animated

    :param user:
    :param technique: Not a dict: a Technique or Item
    :param target:

    :returns:
    """
    technique.advance_round()

    result = technique.use(user, target)

    try:
        tools.load_sound(technique.sfx).play()
    except AttributeError:
        pass

    # action is performed, so now use sprites to animate it
    # this value will be None if the target is off screen
    target_sprite = self._monster_sprite_map.get(target, None)

    # slightly delay the monster shake, so technique animation
    # is synchronized with the damage shake motion
    hit_delay = 0
    if user:
        message = trans(
            "combat_used_x", {"user": user.name, "name": technique.name_trans}
        )

        # TODO: a real check or some params to test if should tackle, etc
        if technique in user.moves:
            hit_delay += 0.5
            user_sprite = self._monster_sprite_map[user]
            self.animate_sprite_tackle(user_sprite)

            if target_sprite:
                self.task(
                    partial(self.animate_sprite_take_damage, target_sprite),
                    hit_delay + 0.2,
                )
                self.task(partial(self.blink, target_sprite), hit_delay + 0.6)

            # Track damage
            self._damage_map[target].add(user)

        else:  # assume this was an item used
            if result:
                message += "\n" + trans("item_success")
            else:
                message += "\n" + trans("item_failure")

        self.alert(message)
        self.suppress_phase_change()

    else:
        if result:
            self.suppress_phase_change()
            self.alert(
                trans(
                    "combat_status_damage",
                    {"name": target.name, "status": technique.name_trans},
                )
            )

    if result and target_sprite and hasattr(technique, "images"):
        tech_sprite = self.get_technique_animation(technique)
        tech_sprite.rect.center = target_sprite.rect.center
        self.task(tech_sprite.image.play, hit_delay)
        self.task(partial(self.sprites.add, tech_sprite, layer=50), hit_delay)
        self.task(tech_sprite.kill, 3)