Moved the CodeUnique validator from an inner class of the CurrencyForm form to an independent class, and removed the annotation future import from the "accounting.currency.forms" module.

src/accounting/currency/forms.py

@@ -17,8 +17,6 @@
 """The forms for the currency management.
 
 """
-from __future__ import annotations
-
 from flask_wtf import FlaskForm
 from wtforms import StringField, ValidationError
 from wtforms.validators import DataRequired, Regexp, NoneOf
@@ -30,22 +28,25 @@ from accounting.utils.strip_text import strip_text
 from accounting.utils.user import get_current_user_pk
 
 
-class CurrencyForm(FlaskForm):
-    """The form to create or edit a currency."""
-    CODE_BLOCKLIST: list[str] = ["create", "store", "exists-code"]
-    """The reserved codes that are not available."""
-
-    class CodeUnique:
+class CodeUnique:
     """The validator to check if the code is unique."""
-        def __call__(self, form: CurrencyForm, field: StringField) -> None:
+
+    def __call__(self, form: FlaskForm, field: StringField) -> None:
         if field.data == "":
             return
+        if not isinstance(form, CurrencyForm):
+            return
         if form.obj_code is not None and form.obj_code == field.data:
             return
         if db.session.get(Currency, field.data) is not None:
             raise ValidationError(lazy_gettext(
                 "Code conflicts with another currency."))
 
+
+class CurrencyForm(FlaskForm):
+    """The form to create or edit a currency."""
+    CODE_BLOCKLIST: list[str] = ["create", "store", "exists-code"]
+    """The reserved codes that are not available."""
     code = StringField(
         filters=[strip_text],
         validators=[DataRequired(lazy_gettext("Please fill in the code.")),