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 __init__(self, *args, **kwargs):
        # If True, avoid entering subdirectories, and match everything recursively,
        # unconditionally.
        self.matchrecursive = False
        # If True, avoid entering subdirectories, and return "unsure" for
        # everything. This is set to True when complex re patterns (potentially
        # including "/") are used.
        self.unsurerecursive = False
        # Patterns for matching paths in this directory.
        self._kindpats = []
        # Glob patterns used to match parent directories of another glob
        # pattern.
        self._globdirpats = []
        super(_tree, self).__init__(*args, **kwargs)