class TileFetcher:
    '''Base class for tile fetchers'''
    
    def __init__(self, tilemanager, *args, **kwargs):
        self.tilemanager = tilemanager
        self._init(*args, **kwargs)
    
    def _init(self):
        return
    
    def upkeep(self):
        '''Do any pending tasks, ie. saving back downloaded images.'''
    
    def has_tile(self, coords):
        '''Check if we can get this tile, without actually doing it'''
        return False
    
    def get_tile(self, coords, block = False):
        '''Fetch a tile described by coords. If there is something that can be done in background (ie. downloading),
        it is controlled by 'block'.
        '''
        
        if self.has_tile(coords):
            return self._get_tile(coords, block)
        else:
            return None
    
    def put_tile(self, coords, image):
        '''Put an image back in the cache, if this class implements such a behaviour.'''
        self._put_tile(coords, image)

    def _put_tile(self, coords, image):
        return