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 render(self, context):
        try:
            if self.params:
                params = template.Variable(self.params).resolve(context)
            else:
                params = {}

            # try matching an address string literal
            email_literal = self.email.strip().lower()
            if EMAIL_RE.match(email_literal):
                email = email_literal
            # treat as a variable
            else:
                email = template.Variable(self.email).resolve(context)
        except template.VariableDoesNotExist:
            return ''

        # now, we generate the gravatar url
        return _build_gravatar_url(email, params)