fix import loop

auto_uncertainties/uncertainty/uncertainty_containers.py

@@ -6,7 +6,7 @@
 import locale
 import math
 import operator
-from typing import Any, Generic, Literal, TypeVar
+from typing import TYPE_CHECKING, Any, Generic, Literal, TypeVar
 import warnings
 
 import joblib
@@ -24,10 +24,9 @@
     ignore_runtime_warnings,
 )
 
-try:
+if TYPE_CHECKING:
     from auto_uncertainties.pint import UncertaintyQuantity
-except ImportError:
-    UncertaintyQuantity = None
+
 
 ERROR_ON_DOWNCAST = False
 COMPARE_RTOL = 1e-9
@@ -256,7 +255,7 @@ def from_string(cls, string: str) -> Uncertainty:
             return cls(float(u1), float(u2))
 
     @classmethod
-    def from_quantities(cls, value, err) -> UncertaintyQuantity | Uncertainty:
+    def from_quantities(cls, value, err) -> UncertaintyQuantity:
         """
         Create an `Uncertainty` object from one or more `pint.Quantity` objects.
 
@@ -284,6 +283,8 @@ def from_quantities(cls, value, err) -> UncertaintyQuantity | Uncertainty:
         value_, err_, units = _check_units(value, err)
         inst = cls(value_, err_)
 
+        from auto_uncertainties.pint import UncertaintyQuantity
+
         if units is not None:
             if UncertaintyQuantity is None:
                 msg = "Failed to load Pint extensions (Pint is not currently installed). Run 'pip install pint' to install it."