Fixup and simplify. Migrations working.

composite_field/base.py

@@ -66,16 +66,14 @@ def contribute_to_class(self, cls, name):
                 self.prefix = '%s_' % name
             for subfield_name, subfield in self.subfields.items():
                 subfield_name = self.prefix + subfield_name
-                verbose_name = subfield.verbose_name
-
-                # If verbose_name is a callable with a single positional
-                # argument or with a parent_verbose_name keyword parameter,
-                # call it with self.verbose_name and update it.
-                if callable(subfield.verbose_name):
-                    try:
-                        subfield.verbose_name = verbose_name(self.verbose_name)
-                    except TypeError:
-                        pass
+
+                if subfield.verbose_name:
+                    # If subfields have a verbose_name set, attempt substitution
+                    # of parent_verbose_name.
+
+                    subfield.verbose_name = subfield.verbose_name % {
+                        "parent_verbose_name": self.verbose_name
+                    }
 
                 subfield.contribute_to_class(cls, subfield_name)
             setattr(cls, name, property(self.get, self.set))

composite_field_test/models.py

@@ -8,7 +8,7 @@
 class CoordField(CompositeField):
     x = models.FloatField(null=True)
     y = models.FloatField(
-        null=True, verbose_name=lambda parent_verbose_name: f"{parent_verbose_name} yyy"
+        null=True, verbose_name="%(parent_verbose_name)s yyy"
     )
 
     class Proxy(CompositeField.Proxy):

docs/source/usage.rst

@@ -91,20 +91,18 @@ return a custom type. A good example for this is the included
 ``ComplexField`` which stores a ``complex`` number in two
 integer fields.
 
-When the ``verbose_name`` on a subfield is callable, it will be called
-with the parent field's ``verbose_name`` so that it can be dynamically set:
+When the ``verbose_name`` is set on a subfield, ``parent_verbose_name``
+will be substituted with the (default) verbose name from the parent field.
 
 .. code-block:: python
 
     class IntegerEstimatedRange(CompositeField):
         minimum = models.DurationField(
-            lambda n: _("%(parent_verbose_name)s minimum") % {
-                "parent_verbose_name": n
-            }
+            verbose_name=_("%(parent_verbose_name)s minimum")
         )
 
     class Species(models.Model):
-        height = IntegerEstimatedRange(verbose_name=_("plant height"))
+        height = IntegerEstimatedRange(verbose_name="plant height")
 
 This will render the verbose name as 'plant height minimum'. Translations
 and internationalisation will function as expected (e.g. in some locales