jinja2.exceptions.TemplateNotFound error

i use flask and i got this error when i call this url: /login Here's my login method:

@app.route('/login')
def login():
	if authenticateForPanel():
		return redirect(url_for("panel"))
	else:
		getParam = request.args.getlist('redirect_uri')
		if getParam:
			ref =getParam[0]
		else:
			ref="/panel"
		return render_template( themesDir + g.blogOptions['active_theme']+'/login.html', blogOptions = g.blogOptions, ref=ref )

And the traceback:

Traceback (most recent call last):
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1701, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1689, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1687, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1360, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1358, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/app.py", line 1344, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/ozcan/Documents/python/app.py", line 209, in login
    return render_template( themesDir + g.blogOptions['active_theme']+'/login.html', blogOptions = g.blogOptions, ref=ref )
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/templating.py", line 124, in render_template
    return _render(ctx.app.jinja_env.get_or_select_template(template_name_or_list),
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/jinja2/environment.py", line 758, in get_or_select_template
    return self.get_template(template_name_or_list, parent, globals)
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/jinja2/environment.py", line 719, in get_template
    return self._load_template(name, self.make_globals(globals))
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/jinja2/environment.py", line 693, in _load_template
    template = self.loader.load(self, name, globals)
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/jinja2/loaders.py", line 115, in load
    source, filename, uptodate = self.get_source(environment, name)
  File "/Users/ozcan/Library/Python/2.7/lib/python/site-packages/flask/templating.py", line 61, in get_source
    raise TemplateNotFound(template)
TemplateNotFound: static/themes/default/login.html

I am absolutely sure the login.html is there(static/themes/default/404.html).Why can this occur?

You put your template in the wrong place. From the Flask docs:

Flask will look for templates in the templates folder. So if your application is a module, this folder is next to that module, if it’s a package it’s actually inside your package: See the docs for more information: http://flask.pocoo.org/docs/quickstart/#rendering-templates

I think you shouldn't prepend themesDir. You only pass the filename of the template to flask, it will then look in a folder called templates relative to your python file.