Python 3 strings contain Unicode code points, not "UTF-8 characters". You can use ord() to get the Unicode code point value, and .encode() to convert it to UTF-8 bytes. Then format each byte as 8-digit binary text, and .join() them together. Example:

# starting and ending code points for 1-, 2-, 3- and 4-byte UTF-8.
s1 = '\x00\x7f\x80\u07ff\u0800\uffff\U00010000\U0010FFFF'

# some printable characters in each range
s2 = 'Aü马🎂'

def utf8_bin(u):
    # format as 8-digit binary, join each byte with space
    return ' '.join([f'{i:08b}' for i in u.encode()])

for u in s1:
    col1 = f'U+{ord(u):04X}' # format Unicode codepoint, leading zeros if <4 digits.
    print(f'{col1:8} {utf8_bin(u)}')

print()

for u in s2:
    col1 = f'U+{ord(u):04X}'
    print(f'{col1:8} {u} {utf8_bin(u)}')

Output:

U+0000   00000000
U+007F   01111111
U+0080   11000010 10000000
U+07FF   11011111 10111111
U+0800   11100000 10100000 10000000
U+FFFF   11101111 10111111 10111111
U+10000  11110000 10010000 10000000 10000000
U+10FFFF 11110100 10001111 10111111 10111111

U+0041   A 01000001
U+00FC   ü 11000011 10111100
U+9A6C   马 11101001 10101001 10101100
U+1F382  🎂 11110000 10011111 10001110 10000010

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'

I recommend using the command-line tool iconv.

For example:

$ iconv option
$ iconv options -f from-encoding -t to-encoding inputfile(s) -o outputfile 

Here is a online tutorial that might be of help:

https://www.tecmint.com/convert-files-to-utf-8-encoding-in-linux/

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.

To convert literal hex to Unicode:

>>> h = '16 03 01 00 e3 01'
>>> h.replace(' ','').decode('hex')
'\x16\x03\x01\x00\xe3\x01'
>>> h.replace(' ','').decode('hex').decode('utf8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "c:\Python27\lib\encodings\utf_8.py", line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: 'utf8' codec can't decode byte 0xe3 in position 4: unexpected end of data
>>>

If the hex were actual utf8, you'd end up with a Unicode string:

>>> h = 'c3 a1'
>>> u = h.replace(' ','').decode('hex').decode('utf8')
>>> u
u'\xe1'
>>> print u
á

You can always map a str to unicode using the latin-1 codec. Once you have a unicode, you can always encode it in utf-8:

data.decode('latin-1').encode("utf-8")

Your utf-8.txt is encoded utf-8-bom which is different from utf-8. For an utf-8-bom file, '\uFEFF' is written into the beginning of the file. Instead of using encoding = 'utf8', try encoding = 'utf-8-sig'

f = open('utf8.txt', mode = 'r', encoding = 'utf-8-sig')
print (f.read())