add @oneshot decorator

masque/error.py

@@ -30,3 +30,10 @@ class PortError(MasqueError):
     Exception raised by builder-related functions
     """
     pass
+
+class OneShotError(MasqueError):
+    """
+    Exception raised when a function decorated with `@oneshot` is called more than once
+    """
+    def __init__(self, func_name: str) -> None:
+        Exception.__init__(self, f'Function "{func_name}" with @oneshot was called more than once')

masque/utils/__init__.py

@@ -5,6 +5,7 @@ from .types import layer_t, annotations_t, SupportsBool
 from .array import is_scalar
 from .autoslots import AutoSlots
 from .deferreddict import DeferredDict
+from .decorators import oneshot
 
 from .bitwise import get_bit, set_bit
 from .vertices import (

masque/utils/decorators.py

@@ -0,0 +1,21 @@
+from typing import Callable
+from functools import wraps
+
+from ..error import OneShotError
+
+
+def oneshot(func: Callable) -> Callable:
+    """
+    Raises a OneShotError if the decorated function is called more than once
+    """
+    expired = False
+
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        nonlocal expired
+        if expired:
+            raise OneShotError(func.__name__)
+        expired = True
+        return func(*args, **kwargs)
+
+    return wrapper