Please show the canonical way to switch between test and production

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Thank you for pyfakefs.

I want to start out from the beginning using pyfakefs the right way.  Please 
show us how to:

* Use pyfakefs during tests
* Not use pyfakefs in production

The *_test.py tests are of course very informative, but they are always in test 
mode.  They do not have a production mode that uses the real file system.

That issue of Testing on the Toilet that introduced pyfakefs would be great.  
Even sample source code somewhere on the net would be sufficient.

I would be using the latest version applicable to Python 2.7.

Stackoverflow issue 
http://stackoverflow.com/questions/16468443/how-to-replace-file-access-reference
s-for-a-module-under-test asks this same question.

Original issue reported on code.google.com by jmcgehe...@gmail.com on 1 Oct 2013 at 10:57