How about this:

>>> ''.join('{:08b}'.format(b) for b in 'سلام'.encode('utf8'))
'1101100010110011110110011000010011011000101001111101100110000101'

This iterates over the encoded bytes object, where you get an integer in the range 0..255 for each iteration. Then the integer is formatted in binary notation with zero padding up to 8 digits. Then glue everything together with str.join().

For the inverse, the approach given in an answer from the question you linked to can be adapted to Python 3 as follows (s is the output of the above example, ie. a str of 0s and 1s):

>>> import re
>>> bytes(int(b, 2) for b in re.split('(........)', s) if b).decode('utf8')
'سلام'

Unicode != UTF-8. UTF-8 is a binary encoding of Unicode, so just write the UTF-8 string just as you would an ASCII string. No need to pack an encoded string either. It's already "just a bunch of bytes".

# coding: utf8
import struct
text = u'我是美国人。'
encoded_text = text.encode('utf8')

# proof packing is redundant...
format = '{0}s'.format(len(encoded_text))
packed_text = struct.pack(format,encoded_text)
print encoded_text == packed_text # result: True

So just encode your Unicode strings and append them to the file after writing your packed ints.

You could try bitarray:

>>> import bitarray
>>> b = bitarray.bitarray()
>>> b.fromstring('a')
>>> b
bitarray('01100001')
>>> b.to01()
'01100001'
>>> b.fromstring('pples')
>>> b.tostring()
'apples'
>>> b.to01()
'011000010111000001110000011011000110010101110011'

You are confusing Unicode with encodings. An encoding is a standard that represents text as within the confines of individual values in the range of 0-255 (bytes), while Unicode is a standard that describes codepoints representing textual glyphs. The two are related but not the same thing.

The Unicode standard includes several encodings. UTF-16 is one such encoding that uses 2 bytes per codepoint, but it is not the only encoding included in the standard. UTF-8 is another such encoding, and it uses a variable number of bytes per codepoint.

Your file, however, is written using ASCII, the default codec used by Python 2 when you do not specify an explicit encoding. If you expected to see 2 bytes per codepoint, encode to UTF-16 explicitly:

fin.write(u'\x40'.encode('utf16-le')

This writes UTF-16 in little endian byte order; there is also a utf16-be codec. Normally, for multi-byte encodings like UTF-16 or UTF32, you'd also include a BOM, or Byte Order Mark; it is included automatically when you write UTF-16 without picking any endianes.

fin.write(u'\x40'.encode('utf16')

I strongly urge you to study up on Unicode, codecs and Python before you continue:

• The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) by Joel Spolsky

• The Python Unicode HOWTO

• Pragmatic Unicode by Ned Batchelder

If you want to post binary data use the base64 encoding.

http://docs.python.org/library/base64.html

Cleaner version:

>>> test_string = '1101100110000110110110011000001011011000101001111101100010101000'
>>> print ('%x' % int(test_string, 2)).decode('hex').decode('utf-8')
نقاب

Inverse (from @Robᵩ's comment):

>>> '{:b}'.format(int(u'نقاب'.encode('utf-8').encode('hex'), 16))
1: '1101100110000110110110011000001011011000101001111101100010101000'