Fix circular imports caused by type annotations

1 files changed, 5 insertions, 1 deletions

diff --git a/polymatrix/expression/mixins/derivativeexprmixin.py b/polymatrix/expression/mixins/derivativeexprmixin.py
index 31a1e31..301166a 100644
--- a/polymatrix/expression/mixins/derivativeexprmixin.py
+++ b/polymatrix/expression/mixins/derivativeexprmixin.py
@@ -1,10 +1,14 @@
+from __future__ import annotations
+
 import abc
 import typing
 
+if typing.TYPE_CHECKING:
+    from polymatrix.expressionstate.abc import ExpressionState
+
 from polymatrix.polymatrix.init import init_poly_matrix
 from polymatrix.expression.mixins.expressionbasemixin import ExpressionBaseMixin
 from polymatrix.polymatrix.abc import PolyMatrix
-from polymatrix.expressionstate.abc import ExpressionState
 from polymatrix.expression.utils.getderivativemonomials import differentiate_polynomial
 from polymatrix.expression.utils.getvariableindices import (
     get_variable_indices_from_variable,