Help me understand this code in pygame please!

#! /usr/bin/env python
import pygame, os
from pygame.locals import *
from sprites import *

def load_level(file):
    img = pygame.image.load(os.path.join("data", file))
    return img.convert()

class Level:

    def __init__(self, level=1):

        self.level = load_level("level.png")

        platform_color = (0, 0, 0, 255)
        collidables = [platform_color]
        self.x = self.y = 0

        while self.y < self.level.get_height():
            color = self.level.get_at((self.x, self.y))
            if color == (0, 255, 0, 255):
                Monster((self.x*24, self.y*24))
            if color == (255, 0, 0, 255):
                HealthUp((self.x*24 + 4, self.y*24 + 4))
            if color == (255, 255, 0, 255):
                Chemical((self.x*24, self.y*24))
            if color == (255, 0, 255, 255):
                AmmoUp((self.x*24, self.y*24))
            if color in collidables:
                top = bottom = left = right = False
                if self.get_tile_above() not in collidables:
                    top = True
                if self.get_tile_under() not in collidables:
                    bottom = True
                if self.get_tile_left() not in collidables:
                    left = True
                if self.get_tile_right() not in collidables:
                    right = True
                Block((self.x*24, self.y*24), top, bottom, left, right)

            self.x += 1
            if self.x >= self.level.get_width():
                self.x = 0
                self.y += 1

    def get_size(self):
        return [self.level.get_size()[0]*24, self.level.get_size()[1]*24]

    def get_tile_above(self):
        try:
            return self.level.get_at((self.x, self.y-1))
        except:
            pass
    def get_tile_under(self):
        try:
            return self.level.get_at((self.x, self.y+1))
        except:
            pass
    def get_tile_left(self):
        try:
            return self.level.get_at((self.x-1, self.y))
        except:
            pass
    def get_tile_right(self):
        try:
            return self.level.get_at((self.x+1, self.y))
        except:
            pass