From 38779470a6d1e818eabf27c7f7cdb3fc6099e344 Mon Sep 17 00:00:00 2001
From: David C Ellis <ducksual@gmail.com>
Date: Fri, 12 Jul 2024 19:43:54 +0100
Subject: [PATCH] Add private parameter to `attribute` to make it easier to
 create cached values.

---
 src/ducktools/classbuilder/prefab.py  | 11 +++++++++++
 src/ducktools/classbuilder/prefab.pyi |  1 +
 tests/prefab/dynamic/test_private.py  | 24 ++++++++++++++++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 tests/prefab/dynamic/test_private.py

diff --git a/src/ducktools/classbuilder/prefab.py b/src/ducktools/classbuilder/prefab.py
index 61c73aa..5ca1e31 100644
--- a/src/ducktools/classbuilder/prefab.py
+++ b/src/ducktools/classbuilder/prefab.py
@@ -294,6 +294,7 @@ def attribute(
     kw_only=False,
     serialize=True,
     exclude_field=False,
+    private=False,
     doc=None,
     type=NOTHING,
 ):
@@ -310,6 +311,7 @@ def attribute(
     :param kw_only: Make this argument keyword only in init
     :param serialize: Include this attribute in methods that serialize to dict
     :param exclude_field: Shorthand for setting repr, compare, iter and serialize to False
+    :param private: Short for init, repr, compare, iter, serialize = False, must have default or factory
     :param doc: Parameter documentation for slotted classes
     :param type: Type of this attribute (for slotted classes)
 
@@ -321,6 +323,15 @@ def attribute(
         iter = False
         serialize = False
 
+    if private:
+        if default is NOTHING and default_factory is NOTHING:
+            raise AttributeError("Private attributes must have defaults or factories.")
+        init = False
+        repr = False
+        compare = False
+        iter = False
+        serialize = False
+
     return Attribute(
         default=default,
         default_factory=default_factory,
diff --git a/src/ducktools/classbuilder/prefab.pyi b/src/ducktools/classbuilder/prefab.pyi
index da9718e..4d7073b 100644
--- a/src/ducktools/classbuilder/prefab.pyi
+++ b/src/ducktools/classbuilder/prefab.pyi
@@ -81,6 +81,7 @@ def attribute(
     kw_only: bool = False,
     serialize: bool = True,
     exclude_field: bool = False,
+    private: bool = False,
 ) -> Attribute: ...
 
 def prefab_gatherer(cls_or_ns: type | MappingProxyType) -> tuple[dict[str, Attribute], dict[str, typing.Any]]: ...
diff --git a/tests/prefab/dynamic/test_private.py b/tests/prefab/dynamic/test_private.py
new file mode 100644
index 0000000..26e1375
--- /dev/null
+++ b/tests/prefab/dynamic/test_private.py
@@ -0,0 +1,24 @@
+from ducktools.classbuilder.prefab import Prefab, attribute, get_attributes
+
+
+def test_private_attribute():
+    class Ex(Prefab):
+        _internal: str | None = attribute(default=None, private=True)
+        a: int
+        b: str
+
+
+    ex = Ex(1, "Hello")
+
+    assert ex.a == 1
+    assert ex.b == "Hello"
+
+    assert ex._internal is None
+
+    _internal_attrib = get_attributes(Ex)["_internal"]
+
+    assert _internal_attrib.init is False
+    assert _internal_attrib.repr is False
+    assert _internal_attrib.iter is False
+    assert _internal_attrib.compare is False
+    assert _internal_attrib.serialize is False