python – Python3 error: initial_value must be str or None, with StringIO-ThrowExceptions

Exception or error:

While porting code from python2 to 3, I get this error when reading from a URL

TypeError: initial_value must be str or None, not bytes.

import urllib
import json
import gzip
from urllib.parse import urlencode
from urllib.request import Request

service_url = ''
text = 'BabelNet is both a multilingual encyclopedic dictionary and a semantic network'
lang = 'EN'
Key  = 'KEY'

    params = {
        'text' : text,
        'key'  : Key,
        'lang' :'EN'


url = service_url + '?' + urllib.urlencode(params)
request = Request(url)
request.add_header('Accept-encoding', 'gzip')
response = urllib.request.urlopen(request)
if'Content-Encoding') == 'gzip':
            buf = StringIO(
            f = gzip.GzipFile(fileobj=buf)
            data = json.loads(

The exception is thrown at this line

buf = StringIO(  

If I use python2, it works fine.

How to solve: returns an instance of bytes while StringIO is an in-memory stream for text only. Use BytesIO instead.

From What’s new in Python 3.0 – Text Vs. Data Instead Of Unicode Vs. 8-bit

The StringIO and cStringIO modules are gone. Instead, import the io module and use io.StringIO or io.BytesIO for text and data respectively.


This looks like another python3 bytes vs. str problem. Your response is of type bytes (which is different in python 3 from str). You need to get it into a string first using'utf-8') say and then use StringIO on it. Or you may want to use BytesIO as someone said – but if you expect it to be str, preferred way is to decode into an str first.


Consider using six.StringIO instead of io.StringIO.

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