A private list variable is inadvertently shared between instance objects

Question

I created many instances of a PlotHandler class. An instance must keep it\'s variables private. But the way I managed them led to a hard to detect problem,

Answer 1

Class attributes are shared between instances. If you want to define an instance attribute (so each object have its own reference to the variable) you have to define it in __init__

class PlotHandler(wx.Frame):
    __crop_section = None
    __projection   = None
    __crop_xcord   = None

    def __init__(self, **kwargs):
        self._band_data = [] #THIS IS NOT SHARED