about Frame.__init__(self)

[yang]

I just a newbie of python
Now I found that almost every program use Tkinter have this line

class xxx(xxx):
    """xxxxx"""

    def __init__(self):
        """xxxxx"""

        Frame.__init__(self)
        .....................
        .......

the line "Frame.__init__(self)" puzzle me.
why use it like this?
can some one explain it?
regards,
yang
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