How to fix: “UnicodeDecodeError: ‘ascii’ codec can’t decode byte”

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Solving problem is about exposing yourself to as many situations as possible like How to fix: “UnicodeDecodeError: ‘ascii’ codec can’t decode byte” and practice these strategies over and over. With time, it becomes second nature and a natural way you approach any problems in general. Big or small, always start with a plan, use other strategies mentioned here till you are confident and ready to code the solution.
In this post, my aim is to share an overview the topic about How to fix: “UnicodeDecodeError: ‘ascii’ codec can’t decode byte”, which can be followed any time. Take easy to follow this discuss.

How to fix: “UnicodeDecodeError: ‘ascii’ codec can’t decode byte”
as3:~/ngokevin-site# nano content/blog/20140114_test-chinese.mkd
as3:~/ngokevin-site# wok
Traceback (most recent call last):
File "/usr/local/bin/wok", line 4, in
Engine()
File "/usr/local/lib/python2.7/site-packages/wok/engine.py", line 104, in init
self.load_pages()
File "/usr/local/lib/python2.7/site-packages/wok/engine.py", line 238, in load_pages
p = Page.from_file(os.path.join(root, f), self.options, self, renderer)
File "/usr/local/lib/python2.7/site-packages/wok/page.py", line 111, in from_file
page.meta['content'] = page.renderer.render(page.original)
File "/usr/local/lib/python2.7/site-packages/wok/renderers.py", line 46, in render
return markdown(plain, Markdown.plugins)
File "/usr/local/lib/python2.7/site-packages/markdown/init.py", line 419, in markdown
return md.convert(text)
File "/usr/local/lib/python2.7/site-packages/markdown/init.py", line 281, in convert
source = unicode(source)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe8 in position 1: ordinal not in range(128). -- Note: Markdown only accepts unicode input!

How to fix it?

In some other python-based static blog apps, Chinese post can be published successfully.
Such as this app: http://github.com/vrypan/bucket3. In my site http://bc3.brite.biz/, Chinese post can be published successfully.

Answer #1:

tl;dr / quick fix

  • Don’t decode/encode willy nilly
  • Don’t assume your strings are UTF-8 encoded
  • Try to convert strings to Unicode strings as soon as possible in your code
  • Fix your locale: How to solve UnicodeDecodeError in Python 3.6?
  • Don’t be tempted to use quick reload hacks

Unicode Zen in Python 2.x – The Long Version

Without seeing the source it’s difficult to know the root cause, so I’ll have to speak generally.

UnicodeDecodeError: 'ascii' codec can't decode byte generally happens when you try to convert a Python 2.x str that contains non-ASCII to a Unicode string without specifying the encoding of the original string.

In brief, Unicode strings are an entirely separate type of Python string that does not contain any encoding. They only hold Unicode point codes and therefore can hold any Unicode point from across the entire spectrum. Strings contain encoded text, beit UTF-8, UTF-16, ISO-8895-1, GBK, Big5 etc. Strings are decoded to Unicode and Unicodes are encoded to strings. Files and text data are always transferred in encoded strings.

The Markdown module authors probably use unicode() (where the exception is thrown) as a quality gate to the rest of the code – it will convert ASCII or re-wrap existing Unicodes strings to a new Unicode string. The Markdown authors can’t know the encoding of the incoming string so will rely on you to decode strings to Unicode strings before passing to Markdown.

Unicode strings can be declared in your code using the u prefix to strings. E.g.

>>> my_u = u'my ünicôdé str?ng'
>>> type(my_u)
<type 'unicode'>

Unicode strings may also come from file, databases and network modules. When this happens, you don’t need to worry about the encoding.

Gotchas

Conversion from str to Unicode can happen even when you don’t explicitly call unicode().

The following scenarios cause UnicodeDecodeError exceptions:

# Explicit conversion without encoding
unicode('€')
# New style format string into Unicode string
# Python will try to convert value string to Unicode first
u"The currency is: {}".format('€')
# Old style format string into Unicode string
# Python will try to convert value string to Unicode first
u'The currency is: %s' % '€'
# Append string to Unicode
# Python will try to convert string to Unicode first
u'The currency is: ' + '€'

Examples

In the following diagram, you can see how the word café has been encoded in either “UTF-8” or “Cp1252” encoding depending on the terminal type. In both examples, caf is just regular ascii. In UTF-8, é is encoded using two bytes. In “Cp1252”, é is 0xE9 (which is also happens to be the Unicode point value (it’s no coincidence)). The correct decode() is invoked and conversion to a Python Unicode is successfull:
Diagram of a string being converted to a Python Unicode string

In this diagram, decode() is called with ascii (which is the same as calling unicode() without an encoding given). As ASCII can’t contain bytes greater than 0x7F, this will throw a UnicodeDecodeError exception:

Diagram of a string being converted to a Python Unicode string with the wrong encoding

The Unicode Sandwich

It’s good practice to form a Unicode sandwich in your code, where you decode all incoming data to Unicode strings, work with Unicodes, then encode to strs on the way out. This saves you from worrying about the encoding of strings in the middle of your code.

Input / Decode

Source code

If you need to bake non-ASCII into your source code, just create Unicode strings by prefixing the string with a u. E.g.

u'Zürich'

To allow Python to decode your source code, you will need to add an encoding header to match the actual encoding of your file. For example, if your file was encoded as ‘UTF-8’, you would use:

# encoding: utf-8

This is only necessary when you have non-ASCII in your source code.

Files

Usually non-ASCII data is received from a file. The io module provides a TextWrapper that decodes your file on the fly, using a given encoding. You must use the correct encoding for the file – it can’t be easily guessed. For example, for a UTF-8 file:

import io
with io.open("my_utf8_file.txt", "r", encoding="utf-8") as my_file:
     my_unicode_string = my_file.read()

my_unicode_string would then be suitable for passing to Markdown. If a UnicodeDecodeError from the read() line, then you’ve probably used the wrong encoding value.

CSV Files

The Python 2.7 CSV module does not support non-ASCII characters ?. Help is at hand, however, with https://pypi.python.org/pypi/backports.csv.

Use it like above but pass the opened file to it:

from backports import csv
import io
with io.open("my_utf8_file.txt", "r", encoding="utf-8") as my_file:
    for row in csv.reader(my_file):
        yield row

Databases

Most Python database drivers can return data in Unicode, but usually require a little configuration. Always use Unicode strings for SQL queries.

MySQL

In the connection string add:

charset='utf8',
use_unicode=True

E.g.

>>> db = MySQLdb.connect(host="localhost", user='root', passwd='passwd', db='sandbox', use_unicode=True, charset="utf8")

PostgreSQL

Add:

psycopg2.extensions.register_type(psycopg2.extensions.UNICODE)
psycopg2.extensions.register_type(psycopg2.extensions.UNICODEARRAY)

HTTP

Web pages can be encoded in just about any encoding. The Content-type header should contain a charset field to hint at the encoding. The content can then be decoded manually against this value. Alternatively, Python-Requests returns Unicodes in response.text.

Manually

If you must decode strings manually, you can simply do my_string.decode(encoding), where encoding is the appropriate encoding. Python 2.x supported codecs are given here: Standard Encodings. Again, if you get UnicodeDecodeError then you’ve probably got the wrong encoding.

The meat of the sandwich

Work with Unicodes as you would normal strs.

Output

stdout / printing

print writes through the stdout stream. Python tries to configure an encoder on stdout so that Unicodes are encoded to the console’s encoding. For example, if a Linux shell’s locale is en_GB.UTF-8, the output will be encoded to UTF-8. On Windows, you will be limited to an 8bit code page.

An incorrectly configured console, such as corrupt locale, can lead to unexpected print errors. PYTHONIOENCODING environment variable can force the encoding for stdout.

Files

Just like input, io.open can be used to transparently convert Unicodes to encoded byte strings.

Database

The same configuration for reading will allow Unicodes to be written directly.

Python 3

Python 3 is no more Unicode capable than Python 2.x is, however it is slightly less confused on the topic. E.g the regular str is now a Unicode string and the old str is now bytes.

The default encoding is UTF-8, so if you .decode() a byte string without giving an encoding, Python 3 uses UTF-8 encoding. This probably fixes 50% of people’s Unicode problems.

Further, open() operates in text mode by default, so returns decoded str (Unicode ones). The encoding is derived from your locale, which tends to be UTF-8 on Un*x systems or an 8-bit code page, such as windows-1251, on Windows boxes.

Why you shouldn’t use sys.setdefaultencoding('utf8')

It’s a nasty hack (there’s a reason you have to use reload) that will only mask problems and hinder your migration to Python 3.x. Understand the problem, fix the root cause and enjoy Unicode zen.
See Why should we NOT use sys.setdefaultencoding(“utf-8”) in a py script? for further details

Answered By: Alastair McCormack

Answer #2:

Finally I got it:

as3:/usr/local/lib/python2.7/site-packages# cat sitecustomize.py
# encoding=utf8  
import sys
reload(sys)
sys.setdefaultencoding('utf8')

Let me check:

as3:~/ngokevin-site# python
Python 2.7.6 (default, Dec  6 2013, 14:49:02)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> reload(sys)
<module 'sys' (built-in)>
>>> sys.getdefaultencoding()
'utf8'
>>>

The above shows the default encoding of python is utf8. Then the error is no more.

Answered By: fisherman

Answer #3:

This is the classic “unicode issue”. I believe that explaining this is beyond the scope of a StackOverflow answer to completely explain what is happening.

It is well explained here.

In very brief summary, you have passed something that is being interpreted as a string of bytes to something that needs to decode it into Unicode characters, but the default codec (ascii) is failing.

The presentation I pointed you to provides advice for avoiding this. Make your code a “unicode sandwich”. In Python 2, the use of from __future__ import unicode_literals helps.

Update: how can the code be fixed:

OK – in your variable “source” you have some bytes. It is not clear from your question how they got in there – maybe you read them from a web form? In any case, they are not encoded with ascii, but python is trying to convert them to unicode assuming that they are. You need to explicitly tell it what the encoding is. This means that you need to know what the encoding is! That is not always easy, and it depends entirely on where this string came from. You could experiment with some common encodings – for example UTF-8. You tell unicode() the encoding as a second parameter:

source = unicode(source, 'utf-8')
Answered By: GreenAsJade

Answer #4:

In some cases, when you check your default encoding (print sys.getdefaultencoding()), it returns that you are using ASCII. If you change to UTF-8, it doesn’t work, depending on the content of your variable.
I found another way:

import sys
reload(sys)
sys.setdefaultencoding('Cp1252')
Answered By: Davy

Answer #5:

I was searching to solve the following error message:

unicodedecodeerror: ‘ascii’ codec can’t decode byte 0xe2 in position 5454: ordinal not in range(128)

I finally got it fixed by specifying ‘encoding’:

f = open('../glove/glove.6B.100d.txt', encoding="utf-8")

Wish it could help you too.

Answered By: Zoe L

Answer #6:

"UnicodeDecodeError: 'ascii' codec can't decode byte"

Cause of this error: input_string must be unicode but str was given

"TypeError: Decoding Unicode is not supported"

Cause of this error: trying to convert unicode input_string into unicode


So first check that your input_string is str and convert to unicode if necessary:

if isinstance(input_string, str):
   input_string = unicode(input_string, 'utf-8')

Secondly, the above just changes the type but does not remove non ascii characters. If you want to remove non-ascii characters:

if isinstance(input_string, str):
   input_string = input_string.decode('ascii', 'ignore').encode('ascii') #note: this removes the character and encodes back to string.
elif isinstance(input_string, unicode):
   input_string = input_string.encode('ascii', 'ignore')

Answer #7:

In order to resolve this on an operating system level in an Ubuntu installation check the following:

$ locale charmap

If you get

locale: Cannot set LC_CTYPE to default locale: No such file or directory

instead of

UTF-8

then set LC_CTYPE and LC_ALL like this:

$ export LC_ALL="en_US.UTF-8"
$ export LC_CTYPE="en_US.UTF-8"
Answered By: vervas

Answer #8:

I find the best is to always convert to unicode – but this is difficult to achieve because in practice you’d have to check and convert every argument to every function and method you ever write that includes some form of string processing.

So I came up with the following approach to either guarantee unicodes or byte strings, from either input. In short, include and use the following lambdas:

# guarantee unicode string
_u = lambda t: t.decode('UTF-8', 'replace') if isinstance(t, str) else t
_uu = lambda *tt: tuple(_u(t) for t in tt)
# guarantee byte string in UTF8 encoding
_u8 = lambda t: t.encode('UTF-8', 'replace') if isinstance(t, unicode) else t
_uu8 = lambda *tt: tuple(_u8(t) for t in tt)

Examples:

text='Some string with codes > 127, like Zürich'
utext=u'Some string with codes > 127, like Zürich'
print "==> with _u, _uu"
print _u(text), type(_u(text))
print _u(utext), type(_u(utext))
print _uu(text, utext), type(_uu(text, utext))
print "==> with u8, uu8"
print _u8(text), type(_u8(text))
print _u8(utext), type(_u8(utext))
print _uu8(text, utext), type(_uu8(text, utext))
# with % formatting, always use _u() and _uu()
print "Some unknown input %s" % _u(text)
print "Multiple inputs %s, %s" % _uu(text, text)
# but with string.format be sure to always work with unicode strings
print u"Also works with formats: {}".format(_u(text))
print u"Also works with formats: {},{}".format(*_uu(text, text))
# ... or use _u8 and _uu8, because string.format expects byte strings
print "Also works with formats: {}".format(_u8(text))
print "Also works with formats: {},{}".format(*_uu8(text, text))

Here’s some more reasoning about this.

Answered By: miraculixx

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