def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def _make_proxy(self, key, match):
        proxy_type = match.group("type")
        key = match.group("key").strip()
        if proxy_type == "env":
            proxy = EnvProxy(key)
        else:
            proxy = ResolverMethodProxy(self._resolver, proxy_type, key)
        filters = [f for f in [rf.strip() for rf in match.group("filters").split("|")] if f]
        for filter_name in filters:
            if filter_name == "jsondecode":
                proxy = JSONDecodeFilter(proxy)
            elif filter_name == "base64decode":
                proxy = Base64DecodeFilter(proxy)
            elif filter_name.startswith("element:"):
                key = filter_name.split(":", 1)[-1]
                proxy = ElementFilter(key, proxy)
            else:
                raise ValueError("Unknown filter %s", filter_name)
        return proxy