code: def context(self, line):
          
          # XXX due to a limitation in Visitor,
          # non-python code after the last python code
          # in a file is not added to self.lines, so we
          # have to guard against IndexErrors.
          idx = line - 1
          if idx >= len(self.lines):
              return self.prefix
          return self.lines[idx]
docs: Return the context for a given 1-offset line number.