'str' does not support the buffer interface Python3 from Python2

Question

Hi have this two funtions in Py2 works fine but it doesn´t works on Py3

def encoding(text, codes):
    binary = ''
    f = open('bytes.bin', 'wb')
    for c in text:
        binary += codes[c]
    f.write('%s' % binary)
    print('Text in binary:', binary)
    f.close()
    return len(binary)

def decoding(codes, large):
    f = file('bytes.bin', 'rb')
    bits = f.read(large)
    tmp = ''
    decode_text = ''
    for bit in bits:
        tmp += bit
        if tmp in fordecodes:
            decode_text += fordecodes[tmp]
            tmp = ''
    f.close()
    return decode_text

The console ouputs this:

Traceback (most recent call last):
  File "Practica2.py", line 83, in <module>
    large = encoding(text, codes)
  File "Practica2.py", line 56, in encoding
    f.write('%s' % binary)
TypeError: 'str' does not support the buffer interface

Answer 1

The fix was simple for me

Use

f = open('bytes.bin', 'w')

instead of

f = open('bytes.bin', 'wb') 

In python 3 'w' is what you need, not 'wb'.

Answer 2

In Python 2, bare literal strings (e.g. 'string') are bytes, whereas in Python 3 they are unicode. This means if you want literal strings to be treated as bytes in Python 3, you always have to explicitly mark them as such.

So, for instance, the first few lines of the encoding function should look like this:

binary = b''
f = open('bytes.bin', 'wb')
for c in text:
    binary += codes[c]
f.write(b'%s' % binary)

and there are a few lines in the other function which need similar treatment.

See Porting to Python 3, and the section Bytes, Strings and Unicode for more details.