def load(self, filename, create_if_missing=True):
        filename = Path(filename)
        if not filename.exists() and create_if_missing:
            self.load_pip_requirements()
            with filename.open("w") as f:
                f.write(yaml.dump(self.serialized, default_flow_style=False,
                                  encoding=None))
            self.filename = filename
            return self.save(filename)
        with filename.open() as f:
            for group, requirements in yaml.load(f.read()).items():
                for requirement in requirements:
                    self[group].add(Requirement.coerce(requirement))
        self.filename = filename
def _search_not(self, base, search_filter, candidates=None):
        # Create empty candidates list as we need to use self.directory for
        # each search
        candidates = list()
        this_filter = list()

        index = 0
        search_filter.remove("!")
        for condition in search_filter:
            if not isinstance(condition, list):
                this_filter.append(condition)
            index +=1

        # Remove this_filter items from search_filter list
        for condition in this_filter:
            search_filter.remove(condition)

        try:
            search_filter = list(search_filter[0])
            for sub_filter in search_filter:
                if not isinstance(sub_filter, list):
                    candidates = self.operation.get(sub_filter)(base,
                                                                search_filter,
                                                                candidates)
                else:
                    candidates = self.operation.get(sub_filter[0])(base,
                                                                   sub_filter,
                                                                   candidates)
        except IndexError:
            pass

        candidates = self._invert_results(candidates)

        for item in this_filter:
            if ">=" in item:
                k, v = item.split(">=")
                candidates = Connection._match_less_than(base, k, v,
                                                            self.directory)
            elif "<=" in item:
                k, v = item.split("<=")
                candidates = Connection._match_greater_than(base, k, v,
                                                         self.directory)
            # Emulate AD functionality, same as "="
            elif "~=" in item:
                k, v = item.split("~=")
                candidates = Connection._match_notequal_to(base, k, v,
                                                         self.directory)
            elif "=" in item:
                k, v = item.split("=")
                candidates = Connection._match_notequal_to(base, k, v,
                                                         self.directory)
        return candidates