Python app engine import issues after app is cached

Question

I'm using a modified version on juno (http://github.com/breily/juno/) in appengine. The problem I'm having is I have code like this:

import juno
import pprint

@get('/')
def home(web):
  pprint.pprint("test")

def main():
  run()
if __name__ == '__main__':
  main()

The first time I start the app up in the dev environment it works fine. The second time and every time after that it can't find pprint. I get this error:

AttributeError: 'NoneType' object has no attribute 'pprint'

If I set the import inside the function it works every time:

@get('/')
def home(web):
  import pprint
  pprint.pprint("test")

So it seems like it is caching the function but for some reason the imports are not being included when it uses that cache. I tried removing the main() function at the bottom to see if that would remove the caching of this script but I get the same problem.

Earlier tonight this code was working fine, I'm not sure what could have changed to cause this. Any insight is appreciated.

Answer 1

Is it possible you are reassigning the name pprint somewhere? The only two ways I know of for a module-level name (like what you get from the import statement) to become None is if you either assign it yourself pprint = None or upon interpreter shutdown, when Python's cleanup assigns all module-level names to None as it shuts things down.

Answer 2

I would leave it that way. I saw a slideshare that Google put out about App Engine optimization that said you can get better performance by keeping imports inside of the methods, so they are not imported unless necessary.