TypeError: 'str' does not support the buffer interface

Question

import hashlib

infile = open("P:\\r.mp3", 'r+b')
data = infile.readline()
hash = hashlib.md5()
hash.update(data)

hash_digest = hash.hexdigest()
print(hash_digest)
#hash_digest = hash_digest.encode('utf-8')
print(hash_digest)
with open("lt.txt", 'ab') as outfile:
    outfile.write(hash_digest + '\n')   #error here

with open("syncDB.txt", 'rb') as fg:
    for data in fg:
    print(data)

outfile.write(hash_digest + '\n')
TypeError: 'str' does not support the buffer interface

How do I correct that and what do I need to learn to see me through these situations?

Also if I encode this in utf-8(uncomment) it gives out the following error:

TypeError: can't concat bytes to str

bignose · Accepted Answer · 2015-10-04 23:55:58Z

23

You're using Python 3, where there is a strict division between text (str) and data (bytes). Text can't be written to a file if you don't explicitly encode it first.

There are two ways to do this:

1) Open the file in text mode (possibly with an encoding specified) so that strings are automatically encoded for you:

with open("lt.txt", 'at', encoding='utf8') as outfile:
    outfile.write(hash_digest + '\n') # or print(hash_digest, file=outfile)

If you don't specify the encoding yourself when opening the file in text mode, the default encoding of your system locale would be used.

2) Encode the strings manually like you tried. But don't try to mix str with bytes like you did, either use a byte literal:

hash_digest = hash_digest.encode('utf-8')
with open("lt.txt", 'ab') as outfile:
    outfile.write(hash_digest + b'\n')   # note the b for bytes

or encode after adding the newline:

    outfile.write((hash_digest + '\n').encode('utf-8'))

edited Oct 4, 2015 at 23:55

bignose

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answered Aug 21, 2011 at 15:47

Rosh Oxymoron

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2 Comments

DSM Over a year ago

You don't need to call f.close() if you're using with-open-as. (Of course I realize you were simply matching the OP's code.)

Grzegorz Wierzowiecki Over a year ago

Thanks ! I had problem with csv.writer , writer.writerow with same error. I've encountered problems adter switching from sys.stdout to file open(). Your solution solved my problems :).

Community · Accepted Answer · 2017-05-23 10:34:15Z

-5

You must search in Google for 'str' does not support the buffer interface

You'll have plenty of answers like this one:

stackoverflow.com/questions/5471158/typeerror-str-does-not-support-the-buffer-interface

And for the second error **TypeError: can't concat bytes to str ** , I think you must write b'\n' in f.write(hex + '\n')

""" edit

yes Rosh Oxymoron is right, b'\n' , and not u'\n'

edited May 23, 2017 at 10:34

CommunityBot

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answered Aug 21, 2011 at 15:54

eyquem

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