Simple context manager to modify and restore user's mmfile search 
  path, if appropriate. This does so without modifying any environment 
  variables.
  This is really unfortunate and fiddly. We can delete this context 
  manager once FFLD-1053 is complete.
    |  | 
        
          | __init__(self,
        selected_opls_dir,
        opls_ver) x.__init__(...) initializes x; see help(type(x)) for signature
 |  |  | 
    |  | 
        
          | __enter__(self) Modify the mmfile path if appropriate.
 |  |  | 
    |  | 
        
          | __exit__(self,
        type,
        value,
        traceback) Restore the original mmfile path.
 |  |  | 
  
    | Inherited from object:__delattr__,__format__,__getattribute__,__hash__,__new__,__reduce__,__reduce_ex__,__repr__,__setattr__,__sizeof__,__str__,__subclasshook__ |