MAINT: refactor design of recursive closures (#11910)

1 files changed, 33 insertions, 1 deletions

diff --git a/numpy/core/_internal.py b/numpy/core/_internal.py
index 48ede14d0..9b8f5aef3 100644
--- a/numpy/core/_internal.py
+++ b/numpy/core/_internal.py
@@ -1,5 +1,5 @@
 """
-A place for code to be called from core C-code.
+A place for internal code
 
 Some things are more easily handled Python.
 
@@ -808,3 +808,35 @@ def _is_from_ctypes(obj):
         return 'ctypes' in ctype_base.__module__
     except Exception:
         return False
+
+
+class recursive(object):
+    '''
+    A decorator class for recursive nested functions.
+    Naive recursive nested functions hold a reference to themselves:
+
+    def outer(*args):
+        def stringify_leaky(arg0, *arg1):
+            if len(arg1) > 0:
+                return stringify_leaky(*arg1)  # <- HERE
+            return str(arg0)
+        stringify_leaky(*args)
+
+    This design pattern creates a reference cycle that is difficult for a
+    garbage collector to resolve. The decorator class prevents the
+    cycle by passing the nested function in as an argument `self`:
+
+    def outer(*args):
+        @recursive
+        def stringify(self, arg0, *arg1):
+            if len(arg1) > 0:
+                return self(*arg1)
+            return str(arg0)
+        stringify(*args)
+
+    '''
+    def __init__(self, func):
+        self.func = func
+    def __call__(self, *args, **kwargs):
+        return self.func(self, *args, **kwargs)
+