code: def pip_r(self, requirements, raise_on_error=True):
          
          cmd = "pip install -r %s" % requirements
          return self.wait(cmd, raise_on_error=raise_on_error)
docs: Install all requirements contained in the given file path
          Waits for command to finish.
  
          Parameters
          ----------
          requirements: str
              Path to requirements.txt
          raise_on_error: bool, default True
              If True then raise ValueError if stderr is not empty