Decorator for a function that causes it to execute only once

Author: emptybutton

sculpting/tools.py

@@ -1,12 +1,12 @@
-from typing import Any
+from typing import Any, Callable
 
-from pyhandling import return_
+from pyhandling import return_, nothing
 from pyhandling.annotations import handler
 
 from sculpting.annotations import attribute_setter
 
 
-__all__ = ("setting_of", )
+__all__ = ("setting_of", "once")
 
 
 def setting_of_attr(attribute_name: str, *, value_transformer: handler = return_) -> attribute_setter:
@@ -23,4 +23,22 @@ def wrapper(object_: object, value: Any) -> Any:
 
         return setattr(object_, attribute_name, value_transformer(value))
 
-    return wrapper
+    return wrapper
+
+
+class once:
+    """
+    Decorator for a function that causes it to execute only once, after which it
+    always returns its result.
+    """
+
+    __result = nothing
+
+    def __init__(self, func: Callable):
+        self._func = func
+
+    def __call__(self, *args, **kwargs) -> Any:
+        if self.__result is nothing:
+            self.__result = self._func(*args, **kwargs)
+
+        return self.__result

tests.py

@@ -1,11 +1,11 @@
 from typing import Any, Type
 
-from pyhandling import by, then, operation_by, execute_operation, to, ArgumentPack
+from pyhandling import times, by, then, operation_by, execute_operation, to, ArgumentPack
 from pytest import mark, raises
 
 from sculpting.annotations import attribute_getter, attribute_setter
 from sculpting.core import *
-from sculpting.tools import setting_of_attr
+from sculpting.tools import setting_of_attr, once
 
 
 class AttributeKeeper:
@@ -29,6 +29,14 @@ def test_setting_of_attr(attribute_name: str, attribute_value: Any):
     assert getattr(obj, attribute_name) == attribute_value
 
 
+def test_once():
+    runner = times(1)
+    once_runner = once(runner)
+
+    assert tuple(once_runner() for _ in range(8)) == (True, ) * 8
+    assert tuple(runner() for _ in range(8)) == (False, True) * 4
+
+
 @mark.parametrize(
     "obj, attribute_getter, result",
     [