How and where in the source code is .loc defined?
 Hi, been browsing through the source code of pandas for the last couple of days, looking for:

**How and where in the source code is `.loc` like in `df.loc['foo']` defined?** 

I found out that the type of a Dataframe `.loc` attribute is `pandas.core.indexing._LocIndexer` but how and where is that implemented?