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The seekable() method of TextIOWrapper always returns False, for it 
does't override the seekable method of IOBase class in which just 
returns False. But, there is a method named _seekable(self) in 
TextIOWrapper(in io.py line 1211):
 def _seekable(self):
 return self._seekable
which should be seekable(self), and _seekable method is overwrited by 
line 1190 in the __init__ method as a bool object:
 self._seekable = self._telling = self.buffer.seekable()