user7031396 user7031396 - 1 year ago 187
Python Question

Python/Flask: UnicodeDecodeError/ UnicodeEncodeError: 'ascii' codec can't decode/encode

Sorry for the millionth question about this, but I've read so much about the topic and still don't get this error fixed (newbie to all of this).
I'm trying to display the content of a postgres table on a website with flask (using Ubuntu 16.04/python 2.7.12). There are non-ascii characters in the table ('ü' in this case) and the result is a UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128).

This is what my looks like:

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

from flask import Blueprint, render_template
import psycopg2
from .forms import Form
from datetime import datetime
from .table import Item, ItemTable

test = Blueprint('test', __name__)

def init_test(app):

def createTable(cur):
cmd = "select * from table1 order by start desc;"
queryResult = cur.fetchall()
items = []
table = 'table could not be read'
if queryResult is not None:
for row in range(0, len(queryResult)):
items.append(Item(queryResult[row][0], queryResult[row][1].strftime("%d.%m.%Y"), queryResult[row][2].strftime("%d.%m.%Y"), \
queryResult[row][1].strftime("%H:%M"), queryResult[row][2].strftime("%H:%M"), \
queryResult[row][3], queryResult[row][4], queryResult[row][5], queryResult[row][6]))
table = ItemTable(items)
return table

def index():
dbcon = psycopg2.connect("dbname=testdb user=postgres host=localhost")
cur = dbcon.cursor()
table = createTable(cur)
return render_template('test_index.html', table=table)

And part of the html-file:

{% extends "layout.html" %}
{% block head %}Title{% endblock %}
{% block body %}
<script type="text/javascript" src="{{ url_for('static', filename='js/bootstrap.js') }}"></script>
<link rel="stylesheet" type="text/css" href="{{ url_for('static', filename='css/custom.css') }}">
<div class="row" id="testid">
{% endblock %}{#
Local Variables:
coding: utf-8
End: #}

The problem is in queryResult[row][6] which is the only row in the table with strings, the rest is integers. The encoding of the postgres database is utf-8. The type of queryResult[row][6] returns type 'str'. What I read here is that the string should be encoded in utf-8, as that is the encoding of the database client. Well, that doesn't seem to work!?
Then I added the line


to force the result to be unicode (type of queryResult[row][6] returned type 'unicode'), because as was recommended here, I tried to stick to unicode everywhere. Well that resulted in a UnicodeEncodeError: 'ascii' codec can't encode character u'\xfc' in position 2: ordinal not in range(128).
Then I thought, maybe something went wrong with converting to string (bytes) before and I tried to do it myself then with writing

queryResult[row][6].encode('utf-8', 'replace')

which led to an UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128). Didn't even work with 'ignore' instead of 'replace'.
What is going on here? I checked if the render_template() has a problem with unicode by creating and passing a variable v=u'ü', but that was no problem and was displayed correctly. Yeah, I read the usual recommended stuff like and Unicode Demystified, but that didn't help me solve my problem here, I'm obviously missing something.

Here is a traceback of the first UnicodeDecodeError:

File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 2000, in __call__
return self.wsgi_app(environ, start_response)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1991, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1567, in handle_exception
reraise(exc_type, exc_value, tb)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1988, in wsgi_app
response = self.full_dispatch_request()
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1641, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1544, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1639, in full_dispatch_request
rv = self.dispatch_request()
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 1625, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/name/Desktop/testFlask/app/test/", line 95, in index
return render_template('test_index.html', table=table) #, var=var
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 134, in render_template
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask/", line 116, in _render
rv = template.render(context)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/jinja2/", line 989, in render
return self.environment.handle_exception(exc_info, True)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/jinja2/", line 754, in handle_exception
reraise(exc_type, exc_value, tb)
File "/home/name/Desktop/testFlask/app/templates/test_index.html", line 1, in top-level template code
{% extends "layout.html" %}
File "/home/name/Desktop/testFlask/app/templates/layout.html", line 40, in top-level template code
{% block body %}{% endblock %}
File "/home/name/Desktop/testFlask/app/templates/test_index.html", line 7, in block "body"
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 86, in __html__
tbody = self.tbody()
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 103, in tbody
out = [ for item in self.items]
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 120, in tr
''.join(, attr) for attr, c in self._cols.items()
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 121, in <genexpr>
File "/home/name/Desktop/testFlask/app/test/", line 7, in td
self.td_contents(item, self.get_attr_list(attr)))
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 99, in td_contents
return self.td_format(self.from_attr_list(item, attr_list))
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/flask_table/", line 114, in td_format
return Markup.escape(content)
File "/home/name/Desktop/testFlask/venv/lib/python2.7/site-packages/markupsafe/", line 165, in escape
rv = escape(s)

Any help is greatly appreciated...

Answer Source

So I finally found a solution after sticking to unicode everywhere with the help of


The error led me then to my own class customCol(Col) that I had written:

class customCol(Col):
def td(self, item, attr):
    return '<td><div id="beschrCol">{}</div></td>'.format(
        self.td_contents(item, self.get_attr_list(attr)))

The problem here was the .format() call, and after reading this, I just turned the string in front of .format to unicode and the problem was solved,

def td(self, item, attr):
    return u'<td><div id="beschrCol">{}</div></td>'.format...

Works with passing strings to Item(), too, but then I had to put


in the Item() call.

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