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 image_url(self, pixel_size=None):
        """
        Get the URL for the user icon in the desired pixel size, if it exists. If no
        size is supplied, give the URL for the full-size image.
        """
        if "profile" not in self._raw:
            return
        profile = self._raw["profile"]
        if (pixel_size):
            img_key = "image_%s" % pixel_size
            if img_key in profile:
                return profile[img_key]
        return profile[self._DEFAULT_IMAGE_KEY]