Error in deployed GAE RequestHandler using Webapp2

Question

I am using the webapp2 framework on Google App Engine, and I'm getting a basic error in one of my Request Handlers.

The app is running ok in the local instance, but causes the following traceback on the deployed version of Google App Engine:

Here's the code:

import os from google.appengine.ext.webapp import template import webapp2 import logging class MainHandler(webapp2.RequestHandler): def get(self): logging.info('hi there 34') template_values = {} self.response.out.write('hello world 4') path = os.path.join(os.path.dirname(__file__), 'index.html') ## This is the code that causes the bug ## self.response.out.write(template.render(path, template_values)) ## ## ## ## debug = os.environ.get('SERVER_SOFTWARE', '').startswith('Dev') app = webapp2.WSGIApplication( [(r'/main', MainHandler)], debug = debug) def main(): app.run()

traceback error:

Traceback (most recent call last): File "/base/python27_runtime/python27_dist/lib/python2.7/wsgiref/handlers.py", line 86, in run self.finish_response() File "/base/python27_runtime/python27_dist/lib/python2.7/wsgiref/handlers.py", line 127, in finish_response self.write(data) File "/base/python27_runtime/python27_dist/lib/python2.7/wsgiref/handlers.py", line 202, in write assert type(data) is StringType,"write() argument must be string" AssertionError: write() argument must be string

What does this error mean?

Ski · Accepted Answer · 2011-12-19 13:42:30Z

2

I think response does not take unicode data, so you have to encode it first:

content = template.render(path, template_values) self.response.out.write(content.encode('utf-8'))

Also I recommend Werkzeug. It works well on appengine and makes life so much easier. It helps to deal with request and response data, url routing, provides http exceptions, has great debugger for offline development and more. I think Werkzeug is a must to have for every python web dev in their toolbox.

edited Dec 19, 2011 at 13:42

answered Dec 19, 2011 at 13:37

Ski

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3 Comments

David Haddad Over a year ago

Thanks for the answer. Typically with GAE, I never had to encode into utf-8. Your answer however did made me think of the html file that is being rendered for the response. My code editor had automatically inserted html markup to make the html into utf-8. And that was the first time I had that markup into an html file and also the first time I see this particular error. But alas, the same error repeats itself with that markup or not. And by encoding as you suggested and without it. I upvoted your answer however because I think it was a good hunch that could benefit others. Any other ideas?

David Haddad Over a year ago

I have just retried this by casting the rendered template value into a string and it worked ok. Not sure however what's the cause as this is the first time that I had to do this. Typically in my previous apps, and also in all the examples on GAE's docs, template.render(path,values) works as it is. Thanks again for pointing me in the text encoding direction!

Ski Over a year ago

Jinja2 does not support utf-8 bytestrings. Template.render always returns unicode string. If you pass non unicode string with non ascii characters to jinja template you will get unicode errors.

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