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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 _getlist(self, key=None, useframes=True, validate=True):
 """Return specified pages as list of TiffPages or TiffFrames. The first item is a TiffPage, and is used as a keyframe for following TiffFrames. """

        getitem = self._getitem
        _useframes = self.useframes

        if key is None:
            key = iter(range(len(self)))
        elif isinstance(key, Iterable):
            key = iter(key)
        elif isinstance(key, slice):
            start, stop, _ = key.indices(2**31-1)
            if not self._indexed and max(stop, start) > len(self.pages):
                self._seek(-1)
            key = iter(range(*key.indices(len(self.pages))))
        elif isinstance(key, inttypes):
            # return single TiffPage
            self.useframes = False
            if key == 0:
                return [self.pages[key]]
            try:
                return [getitem(key)]
            finally:
                self.useframes = _useframes
        else:
            raise TypeError('key must be an integer, slice, or iterable')

        # use first page as keyframe
        keyframe = self._keyframe
        self.keyframe = next(key)
        if validate:
            validate = self._keyframe.hash
        if useframes:
            self.useframes = True
        try:
            pages = [getitem(i, validate) for i in key]
            pages.insert(0, self._keyframe)
        finally:
            # restore state
            self._keyframe = keyframe
            if useframes:
                self.useframes = _useframes

        return pages