subprocess: Calling Popen.communicate() after Popen.stdout.read() returns an empty string

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-07-27.08:26:24.981>
labels = ['type-bug', 'library', '3.10']
title = 'subprocess: Calling Popen.communicate() after Popen.stdout.read() returns an empty string'
updated_at = <Date 2020-08-04.01:55:39.697>
user = 'https://github.com/frostming'

bugs.python.org fields:

activity = <Date 2020-08-04.01:55:39.697>
actor = 'gregory.p.smith'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-07-27.08:26:24.981>
creator = 'Frost Ming'
dependencies = []
files = []
hgrepos = []
issue_num = 41406
keywords = []
message_count = 4.0
messages = ['374366', '374436', '374769', '374783']
nosy_count = 4.0
nosy_names = ['gregory.p.smith', 'vstinner', 'gstarck', 'Frost Ming']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41406'
versions = ['Python 3.10']