def _dict_from_expr(expr, opt):
    if expr.is_commutative is False:
        raise PolynomialError('non-commutative expressions are not supported')

    def _is_expandable_pow(expr):
        return (expr.is_Pow and expr.exp.is_positive and expr.exp.is_Integer
                and expr.base.is_Add)

    if opt.expand is not False:
        try:
            expr = expr.expand()
        except AttributeError:
            raise PolynomialError('expression must support expand method')
        # TODO: Integrate this into expand() itself
        while any(_is_expandable_pow(i) or i.is_Mul and
            any(_is_expandable_pow(j) for j in i.args) for i in
                Add.make_args(expr)):

            expr = expand_multinomial(expr)
        while any(i.is_Mul and any(j.is_Add for j in i.args) for i in Add.make_args(expr)):
            expr = expand_mul(expr)

    if opt.gens:
        rep, gens = _dict_from_expr_if_gens(expr, opt)
    else:
        rep, gens = _dict_from_expr_no_gens(expr, opt)

    return rep, opt.clone({'gens': gens})
Transform an expression into a multinomial form.
dataset/ETHPy150Open sympy/sympy/sympy/polys/polyutils.py/_dict_from_expr