<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_elmt_amt_in_rxt(self, rxt):
 """ Computes total number of atoms in a reaction formula for elements not in external reservoir. This method is used in the calculation of reaction energy per mol of reaction formula. Args: rxt (Reaction):
 a reaction. Returns: Total number of atoms for non_reservoir elements. """

        return sum([rxt.get_el_amount(e) for e in self.pd.elements])