Just a little bit of cleanup.

All I did was update a couple things to be more pythonic.

I moved the import out of the class, which makes ServerProxy and Error available inside \_\_init\_\_ without having to pass them as arguments (not sure why anyone would ever want to pass something different?). 

I also removed the 'return None' from \_\_init\_\_, since an initialized object always returns the object itself, regardless of whether or not you attempt to return something else.

I also would like to offer the suggestion that you refactor the name of the package to either infusionsoftlibrary.py or infusionsoft_library.py, since they both conform to PEP 8.