Merge branch 'master' into fix-issue-10244

1 files changed, 12 insertions, 9 deletions

diff --git a/numpy/core/memmap.py b/numpy/core/memmap.py
index cb025736e..892ad2540 100644
--- a/numpy/core/memmap.py
+++ b/numpy/core/memmap.py
@@ -1,8 +1,8 @@
+from contextlib import nullcontext
+
 import numpy as np
 from .numeric import uint8, ndarray, dtype
-from numpy.compat import (
-    os_fspath, contextlib_nullcontext, is_pathlib_path
-)
+from numpy.compat import os_fspath, is_pathlib_path
 from numpy.core.overrides import set_module
 
 __all__ = ['memmap']
@@ -37,7 +37,10 @@ class memmap(ndarray):
     This class may at some point be turned into a factory function
     which returns a view into an mmap buffer.
 
-    Delete the memmap instance to close the memmap file.
+    Flush the memmap instance to write the changes to the file. Currently there
+    is no API to close the underlying ``mmap``. It is tricky to ensure the
+    resource is actually closed, since it may be shared between different
+    memmap instances.
 
 
     Parameters
@@ -97,7 +100,7 @@ class memmap(ndarray):
     flush
         Flush any changes in memory to file on disk.
         When you delete a memmap object, flush is called first to write
-        changes to disk before removing the object.
+        changes to disk.
 
 
     See also
@@ -109,7 +112,7 @@ class memmap(ndarray):
     The memmap object can be used anywhere an ndarray is accepted.
     Given a memmap ``fp``, ``isinstance(fp, numpy.ndarray)`` returns
     ``True``.
-    
+
     Memory-mapped files cannot be larger than 2GB on 32-bit systems.
 
     When a memmap causes a file to be created or extended beyond its
@@ -148,9 +151,9 @@ class memmap(ndarray):
     >>> fp.filename == path.abspath(filename)
     True
 
-    Deletion flushes memory changes to disk before removing the object:
+    Flushes memory changes to disk in order to read them back
 
-    >>> del fp
+    >>> fp.flush()
 
     Load the memmap and verify data was stored:
 
@@ -220,7 +223,7 @@ class memmap(ndarray):
             raise ValueError("shape must be given")
 
         if hasattr(filename, 'read'):
-            f_ctx = contextlib_nullcontext(filename)
+            f_ctx = nullcontext(filename)
         else:
             f_ctx = open(os_fspath(filename), ('r' if mode == 'c' else mode)+'b')