UnicodeDecodeError while starting the app under Windows with Pycharm

问题

The problem is that when i try to start the application (app.py) i get the following error:

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb3 in position 5: invalid start byte

The whole file app.py:

# -*- 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')

I read somewhere here on stackoverflow that this can help:

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

but it doesn't change anything. Then i changed from

app.run()

app.run(host='127.0.0.1')

but it doesn't work too.

I start the app under windows, so i set the env. variable as follows:

set FLASK_APP = app.py

but no matter if i run this in pycharm or in windows cmd with

flask run

I get the same error everytime.

Full error code:

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:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\site-packages\flask\app.py", line 943, in run
    run_simple(host, port, self, **options)
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\site-packages\werkzeug\serving.py", line 990, in run_simple
    inner()
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\site-packages\werkzeug\serving.py", line 943, in inner
    fd=fd,
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\site-packages\werkzeug\serving.py", line 786, in make_server
    host, port, app, request_handler, passthrough_errors, ssl_context, 
fd=fd
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\site-packages\werkzeug\serving.py", line 679, in __init__
    HTTPServer.__init__(self, server_address, handler)
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\socketserver.py", line 453, in __init__
    self.server_bind()
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\http\server.py", line 138, in server_bind
    self.server_name = socket.getfqdn(host)
  File "C:\Users\Michał\AppData\Local\Programs\Python\Python36- 
32\lib\socket.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

Edit (Update) I changed the python.exe location and project location and the error still exist:

Traceback (most recent call last):
  File "C:/Users/Public/Projekt/main.py", line 11, in <module>
    app.run(host='127.0.0.1')
  File "C:\Users\Public\Python\Python36-32\lib\site- 
packages\flask\app.py", line 943, in run
    run_simple(host, port, self, **options)
  File "C:\Users\Public\Python\Python36-32\lib\site-
packages\werkzeug\serving.py", line 990, in run_simple
    inner()
  File "C:\Users\Public\Python\Python36-32\lib\site-packages\werkzeug\serving.py", line 943, in inner
    fd=fd,
  File "C:\Users\Public\Python\Python36-32\lib\site-packages\werkzeug\serving.py", line 786, in make_server
    host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd
  File "C:\Users\Public\Python\Python36-32\lib\site-packages\werkzeug\serving.py", line 679, in __init__
    HTTPServer.__init__(self, server_address, handler)
  File "C:\Users\Public\Python\Python36-32\lib\socketserver.py", line 453, in __init__
    self.server_bind()
  File "C:\Users\Public\Python\Python36-32\lib\http\server.py", line 138, in server_bind
    self.server_name = socket.getfqdn(host)
  File "C:\Users\Public\Python\Python36-32\lib\socket.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

回答1:

Problem is native letter ł (probably in name Michał) which has code 0xb3 but in Window-1250, not UTF-8.

Maybe you have this letter not only in folder name but also in hostname (computer's name) and then script has problem when it try to get this name in

hostname, aliases, ipaddrs = gethostbyaddr(name)

You can see this line error message.

Maybe if you change hostname in Windows's setting then it will works.

I don't use Windows but when I was using Windows (and DOS) there was always good rule: don't use native (Polish) letters (and spaces) in file/folder name. The same can be with hostname.

Windows may use three different encoding (Code Page) - Window-1250 (CP-1250) for filenames, CP-852 for text in console and UTF-8 in your script. Sometimes also LATIN2 (ISO-8859-2) in old HTML files.

See: image which polish code pages (encodings) on page Python Unicode - decode & encode

回答2:

The method gethostbyaddr will get the name of your computer, if it's not English, cmd will result in this error.

You need to rename your windows computer by english totally, and reboot your computer

来源：https://stackoverflow.com/questions/55782460/unicodedecodeerror-while-starting-the-app-under-windows-with-pycharm

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python

python-3.x

Flask