def _iadd_monom(self, mc):
        if self in self.ring._gens_set:
            cpself = self.copy()
        else:
            cpself = self
        expv, coeff = mc
        c = cpself.get(expv)
        if c is None:
            cpself[expv] = coeff
        else:
            c += coeff
            if c:
                cpself[expv] = c
            else:
                del cpself[expv]
        return cpself
add to self the monomial coeff*x0**i0*x1**i1*...
dataset/ETHPy150Open sympy/sympy/sympy/polys/rings.py/PolyElement._iadd_monom