If you're using Flask, you can redefine the delimiters used by Jinja:
class CustomFlask(Flask):
jinja_options = Flask.jinja_options.copy()
jinja_options.update(dict(
variable_start_string='%%', # Default is '{{', I'm changing this because Vue.js uses '{{' / '}}'
variable_end_string='%%',
))
app = CustomFlask(__name__) # This replaces your existing "app = Flask(__name__)"