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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def scroll(self, rect, dx, dy, attr=None, fill=' '):
        u'''Scroll a rectangle.'''
        if attr is None:
            attr = self.attr
        x0, y0, x1, y1 = rect
        source = SMALL_RECT(x0, y0, x1 - 1, y1 - 1)
        dest = self.fixcoord(x0 + dx, y0 + dy)
        style = CHAR_INFO()
        style.Char.AsciiChar = ensure_str(fill[0])
        style.Attributes = attr

        return self.ScrollConsoleScreenBufferW(self.hout, byref(source), 
                                          byref(source), dest, byref(style))