Django: singleton per request?

We have a wrapper around a suds (SOAP) request, that we use like this throughout our app:

from app.wrapper import ByDesign
bd = ByDesign()

Unfortunately, this instantiation is made at several points per request, causing suds to redownload the WSDL file, and I think we could save some time by making bd = ByDesign() return a singleton.

Since suds is not threadsafe, it'd have to be a singleton per request.

The only catch is, I'd like to make it so I don't have to change any code other than the app.wrapper.ByDesign class, so that I don't have to change any code that calls it. If there wasn't the 'singleton per request' requirement, I'd do开发者_运维问答 something like this:

class ByDesignRenamed(object):
    pass

_BD_INSTANCE = None
def ByDesign():
    global _BD_INSTANCE
    if not _BD_INSTANCE:
       _BD_INSTANCE = ByDesignRenamed()
    return _BD_INSTANCE

But, this won't work in a threaded server environment. Any ideas for me?

Check out threading.local(), which is somewhere between pure evil and the only way to get things going. It should probably be something like this:

import threading

_local = threading.local()

def ByDesign():
    if 'bd' not in _local.__dict__:
       _local.bd = ByDesignRenamed()
    return _local.bd

Further reading:

• Why is using thread locals in Django bad?
• Thread locals in Python - negatives, with regards to scalability?