From 2cf77a5a70c1c6fa49366d5decd9d59caa40f78c Mon Sep 17 00:00:00 2001
From: Ali Ebrahim <aebrahim@users.noreply.github.com>
Date: Tue, 9 Jan 2024 20:42:39 +0000
Subject: [PATCH] Add support for `@property` for once_per_instance.

---
 once/__init__.py | 11 ++++++++++-
 once_test.py     | 19 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/once/__init__.py b/once/__init__.py
index e07ead0..937d710 100644
--- a/once/__init__.py
+++ b/once/__init__.py
@@ -15,7 +15,7 @@
 
 def _is_method(func: collections.abc.Callable):
     """Determine if a function is a method on a class."""
-    if isinstance(func, (classmethod, staticmethod)):
+    if isinstance(func, (classmethod, staticmethod, property)):
         return True
     sig = inspect.signature(func)
     return "self" in sig.parameters
@@ -309,6 +309,8 @@ def __get__(self, obj, cls) -> collections.abc.Callable:
 class once_per_instance:  # pylint: disable=invalid-name
     """A version of once for class methods which runs once per instance."""
 
+    is_property: bool
+
     @classmethod
     def with_options(cls, per_thread: bool = False, retry_exceptions=False):
         return lambda func: cls(func, per_thread=per_thread, retry_exceptions=retry_exceptions)
@@ -339,6 +341,11 @@ def once_factory(self) -> _ONCE_FACTORY_TYPE:
     def _inspect_function(self, func: collections.abc.Callable):
         if isinstance(func, (classmethod, staticmethod)):
             raise SyntaxError("Must use @once.once_per_class on classmethod and staticmethod")
+        if isinstance(func, property):
+            func = func.fget
+            self.is_property = True
+        else:
+            self.is_property = False
         if not _is_method(func):
             raise SyntaxError(
                 "Attempting to use @once.once_per_instance method-only decorator "
@@ -357,4 +364,6 @@ def __get__(self, obj, cls) -> collections.abc.Callable:
                     bound_func, self.once_factory(), self.fn_type, self.retry_exceptions
                 )
                 self.callables[obj] = callable
+        if self.is_property:
+            return callable()
         return callable
diff --git a/once_test.py b/once_test.py
index 84c7e75..81bc420 100644
--- a/once_test.py
+++ b/once_test.py
@@ -835,6 +835,25 @@ def execute(i):
         self.assertEqual(min(results), 1)
         self.assertEqual(max(results), math.ceil(_N_WORKERS / 4))
 
+    def test_once_per_instance_property(self):
+        counter = Counter()
+
+        class _CallOnceClass:
+            @once.once_per_instance
+            @property
+            def value(self):
+                nonlocal counter
+                return counter.get_incremented()
+
+        a = _CallOnceClass()
+        b = _CallOnceClass()
+        self.assertEqual(a.value, 1)
+        self.assertEqual(b.value, 2)
+        self.assertEqual(a.value, 1)
+        self.assertEqual(b.value, 2)
+        self.assertEqual(_CallOnceClass().value, 3)
+        self.assertEqual(_CallOnceClass().value, 4)
+
     def test_once_per_class_classmethod(self):
         counter = Counter()