[Python] python http.server hangs when running cgi code in ubuntu

Sorry for the possible duplication of the question. I'm using python 3.7 http.server (python -m http.server --cgi 8080) to test the webserver locally, it works fine under Windows (and under Ubuntu on the server where nginx is running). But when I use it under Ubuntu, my cgi code hangs at the line where the code reads the input: sys.stdin.readline() (or for sys.stdin.read()). When I remove this line (put the string with some input) it works.

The code of cgi-file looks like:

#!/usr/bin/env python3
# coding: utf-8

import os
import sys
import json

# trace cgi errors
import traceback

import codecs
from collections import namedtuple
from time import process_time
from datetime import datetime
import cgi


sys.stderr = sys.stdout
try:
json_inputdata = sys.stdin.readline()
# Parse JSON into an object with attributes corresponding to dict keys.
InputData = json.loads(json_inputdata, object_hook=lambda d: namedtuple('InputData', d.keys())(*d.values()))

...

except:
print("\n\n<PRE>")
traceback.print_exc()


Maybe someone knows what the problem is? Thanks in advance.

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