Improve type checking in conversions.py

gmso/utils/conversions.py

@@ -1,5 +1,6 @@
 """Module for standard conversions needed in molecular simulations."""
-
+from __future__ import annotations
+from typing import TYPE_CHECKING
 import re
 from functools import lru_cache
 
@@ -9,7 +10,9 @@
 import unyt as u
 from unyt.dimensions import length, mass, time
 
-import gmso
+if TYPE_CHECKING:
+        import gmso
+
 from gmso.exceptions import EngineIncompatibilityError, GMSOError
 from gmso.lib.potential_templates import (
     PotentialTemplate,
@@ -57,7 +60,7 @@ def _try_sympy_conversions(pot1, pot2):
 
 def _conversion_from_template_name(
     top, connStr: str, conn_typeStr: str, convStr: str
-) -> gmso.Topology:
+) -> 'gmso.Topology':
     """Use the name of convStr to identify function to convert sympy expressions."""
     conversions_map = {  # these are predefined between template types
         # More functions, and `(to, from)` key pairs added to this dictionary
@@ -101,7 +104,7 @@ def _conversion_from_template_name(
 
 
 def _conversion_from_template_obj(
-    top: gmso.Topology,
+    top: 'gmso.Topology',
     connStr: str,
     conn_typeStr: str,
     potential_template: gmso.core.ParametricPotential,