Jinja2 custom code generator to detect unused variables

codegenerator.py

from jinja2.compiler import CodeGenerator

class CustomCodeGenerator(CodeGenerator):

    def __init__(self, *args, **kwargs):
        super(CustomCodeGenerator, self).__init__(*args, **kwargs)
        self._vars_tracker = set()

    def visit_Template(self, *args, **kwargs):
        super(CustomCodeGenerator, self).visit_Template(*args, **kwargs)
        if len(self._vars_tracker) > 0:
            warn('unused variables: {0}'.format(', '.join(self._vars_tracker)))

    def visit_Name(self, node, frame):
        if node.ctx == 'store':
            self._vars_tracker.add(node.name)
        elif node.ctx == 'load':
            self._vars_tracker.discard(node.name)
        super(CustomCodeGenerator, self).visit_Name(node, frame)