Fixes issue #19506: Use a memoryview to avoid a data copy when piping data

to stdin within subprocess.Popen.communicate.  5-10% less cpu usage.

Lib/subprocess.py

@@ -1562,6 +1562,9 @@ class Popen(object):
 
             self._save_input(input)
 
+            if self._input:
+                input_view = memoryview(self._input)
+
             with _PopenSelector() as selector:
                 if self.stdin and input:
                     selector.register(self.stdin, selectors.EVENT_WRITE)
@@ -1583,8 +1586,8 @@ class Popen(object):
 
                     for key, events in ready:
                         if key.fileobj is self.stdin:
-                            chunk = self._input[self._input_offset :
-                                                self._input_offset + _PIPE_BUF]
+                            chunk = input_view[self._input_offset :
+                                               self._input_offset + _PIPE_BUF]
                             try:
                                 self._input_offset += os.write(key.fd, chunk)
                             except OSError as e:

Misc/NEWS

@@ -18,6 +18,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #19506: Use a memoryview to avoid a data copy when piping data
+  to stdin within subprocess.Popen.communicate.  5-10% less cpu usage.
+
 - Issue #19876: selectors unregister() no longer raises ValueError or OSError
   if the FD is closed (as long as it was registered).