docs: def create(self, name, description=None, units=None,
                 agg_method="priority_fill", overwrite=False):
          """ Create, or get if exists, a Symbol.
          
          Parameters
          ----------
          name : str
              A symbol's name is a primary key, used across
              the Trump ORM.
          description : str, optional
              An arbitrary string, used to store user information
              related to the symbol.
          units : str, optional
              This is a string used to denote the units of the final
              data Series.
          agg_method : str, optional
              The aggregation method, used to calculate
              the final feed.  Defaults to priority_fill.
          overwrite : bool, optional
              Set to True, to force deletion an existing symbol.
              defaults to False.
              
          Returns
          -------
          Symbol
          """
          sym = self.try_to_get(name)
  
          if sym is not None:
              if overwrite:
                  print "Deleting {}".format(sym.name)
                  self.ses.delete(sym)
                  self.ses.commit()
              else:
                  msg = 'Symbol {} already exists.\n' + \
                        'Consider setting overwrite to True.'
                  msg = msg.format(name)
                  raise Exception(msg)
  
          sym = Symbol(name, description, units, agg_method)
          
          self.ses.add(sym)
  
          print "Creating {}".format(sym.name)
          sym.add_alias(name)
  
          sym.handle = SymbolHandle(sym=sym)
          self.ses.commit()
  
          return sym