Python3 error: initial_value must be str or None, with StringIO

Question

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 = 'https://babelfy.io/v1/disambiguate'
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 response.info().get('Content-Encoding') == 'gzip':
            buf = StringIO(response.read())
            f = gzip.GzipFile(fileobj=buf)
            data = json.loads(f.read())

The exception is thrown at this line

buf = StringIO(response.read())

If I use python2, it works fine.

It just gives this error and halts. TypeError: initial_value must be unicode or None, not str — AMisra
– AMisra, Commented Jun 26, 2015 at 4:52
can you include the value of your variable url? when I try it with url = 'http://www.google.com' the code runs fine for me — maxymoo
– maxymoo, Commented Jun 26, 2015 at 5:18
To anyone coming here due to pandas.read_csv() hiccuping on inferring the wrong encoding on ASCII input, use encoding='utf8' or 'latin1' to force it. — smci
– smci, Commented Mar 26, 2020 at 21:14

tynn · Accepted Answer · 2015-06-26 07:37:10Z

151

response.read() 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.

edited Jun 26, 2015 at 7:37

answered Jun 26, 2015 at 7:28

tynn

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Comments

gabhijit · Accepted Answer · 2015-06-26 07:31:55Z

29

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 response.read().decode('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.

answered Jun 26, 2015 at 7:31

gabhijit

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1 Comment

Brian Wiley Over a year ago

i think this is best answer for modules that can only read from StringIO and BytesIO such as Bio.SeqIO as in records = SeqIO.parse(StringIO(r.read().decode('utf-8')), "fasta")

Max Bileschi · Accepted Answer · 2019-07-08 17:05:28Z

3

Consider using six.StringIO instead of io.StringIO.

answered Jul 8, 2019 at 17:05

Max Bileschi

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Comments

eluri saichand · Accepted Answer · 2021-09-24 19:32:27Z

0

And if you are migrating code from python2 to python3 and using suds old version use "suds-py3" for python3

answered Sep 24, 2021 at 19:32

eluri saichand

1

2 Comments

Community Over a year ago

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Wizard.Ritvik Over a year ago

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