code: def get_aliasing(*extra):
      
      alias = dict((k, k) for k in funcs_common)
      alias.update(_alias_str)
      alias.update((fn, fn) for fn in _alias_builtin.values())
      alias.update(_alias_builtin)
      for d in extra:
          alias.update(d)
      alias.update((k, k) for k in set(alias.values()))
      # Treat nan-functions as firstclass member and add them directly
      for key in set(alias.values()):
          if key not in funcs_no_separate_nan:
              key = 'nan' + key
              alias[key] = key
      return alias
docs: The assembles the dict mapping strings and functions to the list of
      supported function names:
              e.g. alias['add'] = 'sum'  and alias[sorted] = 'sort'
      This funciton should only be called during import.