# -*- coding: utf-8 -*-
from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    return 'Hello World'

if __name__ == "__main__":
    app.run(host='127.0.0.1')

# -*- coding: utf-8 -*-

app.run()

app.run(host='127.0.0.1')

set FLASK_APP = app.py

flask run

Traceback (most recent call last):
  File "C:/Users/Michał/Desktop/Michał/Zadanie/Flask_Blog/app.py",
line 11, in <module>
    app.run(host='127.0.0.1')
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsite-packagesflaskapp.py", line 943, in run
    run_simple(host, port, self, **options)
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsite-packageswerkzeugserving.py", line 990, in run_simple
    inner()
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsite-packageswerkzeugserving.py", line 943, in inner
    fd=fd,
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsite-packageswerkzeugserving.py", line 786, in make_server
    host, port, app, request_handler, passthrough_errors, ssl_context,
fd=fd
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsite-packageswerkzeugserving.py", line 679, in __init__
    HTTPServer.__init__(self, server_address, handler)
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsocketserver.py", line 453, in __init__
    self.server_bind()
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libhttpserver.py", line 138, in server_bind
    self.server_name = socket.getfqdn(host)
  File "C:UsersMichałAppDataLocalProgramsPythonPython36-
32libsocket.py", line 673, in getfqdn
    hostname, aliases, ipaddrs = gethostbyaddr(name)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb3 in position 5:
invalid start byte