Use LazyFormat to fix infinite loop

Author: Matthias Koeppe

src/sage/rings/number_field/number_field.py

@@ -1913,7 +1913,9 @@ def _Hom_(self, codomain, category=None):
             True
         """
         if not is_NumberFieldHomsetCodomain(codomain):
-            raise TypeError("{} is not suitable as codomain for homomorphisms from {}".format(codomain, self))
+            # Using LazyFormat fixes #28036 - infinite loop
+            from sage.misc.lazy_format import LazyFormat
+            raise TypeError(LazyFormat("%s is not suitable as codomain for homomorphisms from %s") % (codomain, self))
         from .morphism import NumberFieldHomset
         return NumberFieldHomset(self, codomain, category)