code: def trace(self, name, chain=-1):
          
          if isinstance(name, str):
              return self.db.trace(name, chain)
          elif isinstance(name, Variable):
              return self.db.trace(name.__name__, chain)
          else:
              raise ValueError(
                  'Name argument must be string or Variable, got %s.' %
                  name)
docs: Return the trace of a tallyable object stored in the database.
  
          :Parameters:
          name : string
            The name of the tallyable object.
          chain : int
            The trace index. Setting `chain=i` will return the trace created by
            the ith call to `sample`.