Making templatetags on App Engine is a bit different from the real django. Here is how i made mine.

* Create a templatetags folder under your root folder
* Create a empty file named __init__.py
* Create your templatetags file, for this example we will use ads_manager.py
Open your ads_manager.py and enter the following code
from google.appengine.ext.webapp import template
register = template.create_template_register()
def checkShowAds(remote_add):
if remote_add == "127.0.0.1":
return ""
else:
return "ADS HERE"
register.filter("checkShowAds",checkShowAds)

from google.appengine.ext.webapp import template
– means import the template class from the package google…

register = template.create_template_register()
– register this template or something like that

def checkShowAds(remote_add):……………..
– our function

register.filter(”checkShowAds”,checkShowAds)
– add our function as custom filter

Next stop is to open your python file that you will use this templatetags/filter
and insert the following code
from google.appengine.ext.webapp import template
template.register_template_library('templatetags.ads_manager')
class MainPage(webapp.RequestHandler):
def get(self):
template_values = {
'remote_add': self.request.remote_addr
}
directory = os.path.dirname(__file__)
path = os.path.join(directory,os.path.join('templates','index.html'))
self.response.out.write(template.render(path,template_values))

template.register_template_library(’templatetags.ads_manager’)
– What this do is that it register your templatetags so you can use it on your template/view.

class MainPage(webapp.RequestHandler):……
– This and the rest of the code will just render your template while passing the remote address as ‘remote_add’ variable

Next is to open your template and add the following:
{{ remote_add|checkShowAds }}

I hope this helps. It took me days to understand the basic concept of how templatetags on app engine works.