human
Write me a the Python code you requested given the following:
Solve in Python:
This kata is inspired by Tower Defense (TD), a subgenre of strategy video games where the goal is to defend a player's territories or possessions by obstructing enemy attackers, usually by placing defensive structures on or along their path of attack.

Objective
It's the future, and hostile aliens are attacking our planet. We've set up a defense system in the planet's outer perimeter. You're tasked with calculating the severity of a breach.
Input
Your function will receive three arguments:

Battle Area Map: An array/list of strings representing an n x n battle area.
        Each string will consist of any of the following characters:

0: entrance point (starting position on alien path)
1: alien path
" "(space character): not alien path
A - Z: turret positions

Turret Stats: An object/dict where keys are upper-case characters from the English alphabet (A - Z) and the values are subarrays in the following format:
[n,m] - where n is the attack range of a turret, and m is its shot frequency per move
Alien Wave Stats: An array of integers representing each individual alien in sequence. Each value is an integer representing the health points of each alien.
health points are the number of turret shots required to take down a given alien. Integer zero (0) counts as a gap in sequence.

Output
Return the integer sum of total health points of all aliens that successfully penetrate our defense.


The image above shows the game state for the test example (below) at the 11th move.
The green square in the north-west quadrant represents the starting position of the alien wave, and the red square in the south-east quadrant represents the last position before breaching the defensive perimeter.
The blue circles represent the turret positions and are labeled A,B,C, and D.
The red alien is the first alien in the sequence.
Technical Details

There is only one path and it maintains a width of 1.
Aliens move one square per turn
Turrets only fire toward enemies in range.
        In the image above, the turret labeled A has the...
assistant
#Here is the Python code you requested.

class Turret:
    def __init__(self, tid, r, c, size, info):
        self.tid = tid
        self.attack = info[1]
        self.targets = set()
        atkRange = info[0]
        for dr in range(-atkRange, atkRange + 1):
            for dc in range(-atkRange, atkRange + 1):
                if dr == 0 and dc == 0:
                    continue
                ra, ca = r + dr, c + dc
                if not(0 <= ra < size and 0 <= ca < size):
                    continue
                if dr * dr + dc * dc <= atkRange * atkRange:
                    self.targets.add((ra, ca))

class Alien:
    def __init__(self, pathIdx, pos, hp):
        self.pathIdx = pathIdx
        self.pos = pos
        self.hp = hp

def tower_defense(grid, _turrets, _wave):
    answer = 0
    size = len(grid)
    lWave = len(_wave)
    wave = _wave[:]
    ones = set()
    turrets, aliens = [], []
    for r, row in enumerate(grid):
        for c, square in enumerate(row):
            if square == "1":
                ones.add((r, c))
            elif square.isalpha():
                turrets.append(Turret(square, r, c, size, _turrets[square]))
            elif square == "0":
                start = (r, c)
    for turret in turrets:
        turret.targets = turret.targets & (ones | {start})
    turrets.sort(key = lambda t: t.tid)
    path = [start]
    r, c = start
    while ones:
        for r1, c1 in ones:
            if abs(r1 - r) + abs(c1 - c) == 1:
                path.append((r1, c1))
                ones.discard((r1, c1))
                r, c = r1, c1
                break
    lPath = len(path)
    time = -1
    while time < lWave or aliens:
        time += 1
        for i in range(len(aliens) - 1, -1, -1):
            alien = aliens[i]
            if alien.hp <= 0:
                del aliens[i]
                continue
            alien.pathIdx += 1
            if alien.pathIdx == lPath:
                answer += alien.hp
                del aliens[i]
                continue
            alien.pos = path[alien.pathIdx]
        if...