bpo-31065: Add doc about Popen.poll returning None. (GH-3169)

(cherry picked from commit 006617ff7d6df3fdedcfe53e94ee2c52cc796437)

diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 27f3e825961e1a1b7d6a8f1c3de2894c848926c0..ea7e664f578bbc0fb8de64886ea9e28ff8b5a45d 100644 (file)
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -584,7 +584,7 @@ Instances of the :class:`Popen` class have the following methods:
 .. method:: Popen.poll()
 
    Check if child process has terminated.  Set and return
-   :attr:`~Popen.returncode` attribute.
+   :attr:`~Popen.returncode` attribute. Otherwise, returns ``None``.
 
 
 .. method:: Popen.wait(timeout=None)