code: def getch(self):
          
          self.pos += 1
          return self.string[self.pos - 1:self.pos]
docs: Get a single character and advance the scan pointer.
  
              >>> s = Scanner("abc")
              >>> s.getch()
              'a'
              >>> s.getch()
              'b'
              >>> s.getch()
              'c'
              >>> s.pos
              3