def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def exceptions_log_path(cls, for_pid=None, in_dir=None):
        """Get the path to either the shared or pid-specific fatal errors log file."""
        if for_pid is None:
            intermediate_filename_component = ""
        else:
            assert isinstance(for_pid, Pid)
            intermediate_filename_component = ".{}".format(for_pid)
        in_dir = in_dir or cls._log_dir
        return os.path.join(
            in_dir, ".pids", "exceptions{}.log".format(intermediate_filename_component)
        )