def pip_r(self, requirements, raise_on_error=True):
cmd = "<STR_LIT>" % requirements<EOL>return self.wait(cmd, raise_on_error=raise_on_error)<EOL>
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