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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 _pad(self, a, axis, extrap, out):
 """Add padding to an array. Parameters array to be padded to size `N` axis : int axis along which to pad extrap : {bool, 'const'} or 2-tuple Method to extrapolate `a`. For a 2-tuple, the two elements are for the left and right pads, whereas a single value applies to both ends. Options are: * True: power-law extrapolation using the end segment * False: zero padding * 'const': constant padding with the end point value out : bool pad the output if True, otherwise the input; the two cases have their left and right pad sizes reversed """


        assert a.shape[axis] == self.Nin

        axis %= a.ndim  # to fix the indexing below with axis+1

        to_axis = [1] * a.ndim
        to_axis[axis] = -1

        Npad = self.N - self.Nin
        if out:
            _Npad, Npad_ = Npad - Npad//2, Npad//2
        else:
            _Npad, Npad_ = Npad//2, Npad - Npad//2

        try:
            _extrap, extrap_ = extrap
        except (TypeError, ValueError):
            _extrap = extrap_ = extrap

        if isinstance(_extrap, bool):
            if _extrap:
                end = np.take(a, [0], axis=axis)
                ratio = np.take(a, [1], axis=axis) / end
                exp = np.arange(-_Npad, 0).reshape(to_axis)
                _a = end * ratio ** exp
            else:
                _a = np.zeros(a.shape[:axis] + (_Npad,) + a.shape[axis+1:])
        elif _extrap == 'const':
            end = np.take(a, [0], axis=axis)
            _a = np.repeat(end, _Npad, axis=axis)
        else:
            raise ValueError("left extrap not supported")
        if isinstance(extrap_, bool):
            if extrap_:
                end = np.take(a, [-1], axis=axis)
                ratio = end / np.take(a, [-2], axis=axis)
                exp = np.arange(1, Npad_ + 1).reshape(to_axis)
                a_ = end * ratio ** exp
            else:
                a_ = np.zeros(a.shape[:axis] + (Npad_,) + a.shape[axis+1:])
        elif extrap_ == 'const':
            end = np.take(a, [-1], axis=axis)
            a_ = np.repeat(end, Npad_, axis=axis)
        else:
            raise ValueError("right extrap not supported")

        return np.concatenate((_a, a, a_), axis=axis)