mod_cgi + utf8 + Python3 produces no output

Question

If you create this app.py

#!/usr/bin/python3
print(\"Content-Type: text/plain;charset=utf-8\\n\")
print(\"Hello World!\")

and

Answer 1

Easy solution

Just add:

SetEnv PYTHONIOENCODING utf8

in the .htaccess, along with:

Options +ExecCGI
AddHandler cgi-script .py

See also overwrite python3 default encoder when using apache server and Problème python apache et utf8. Also related but no answers did directly solve it: Set encoding in Python 3 CGI scripts.

Alternate solution

For Python 3 - 3.6 (see How to set sys.stdout encoding in Python 3?):

import sys, codecs
sys.stdout = codecs.getwriter("utf-8")(sys.stdout.detach())

For Python 3.7+:

sys.stdout.reconfigure(encoding='utf-8')

---

Note: even if it is sometimes cited in some answers, the following script does not work with Apache 2.4 + mod_cgi + Python3:

import locale                                  # Ensures that subsequent open()s 
locale.getpreferredencoding = lambda: 'UTF-8'  # are UTF-8 encoded.
import sys
sys.stdin = open('/dev/stdin', 'r')            # Re-open standard files in UTF-8 
sys.stdout = open('/dev/stdout', 'w')          # mode.
sys.stderr = open('/dev/stderr', 'w') 
print("Content-Type: text/plain;charset=utf-8\n")
print(str(sys.stdout.encoding))  # I still get: ANSI_X3.4-1968