Convert UTF-16 to UTF-8 and remove BOM?

Question

We have a data entry person who encoded in UTF-16 on Windows and would like to have utf-8 and remove the BOM. The utf-8 conversion works but BOM is still there. How would I remove this? This is what I currently have:

batch_3={'src':'/Users/jt/src','dest':'/Users/jt/dest/'}
batches=[batch_3]

for b in batches:
  s_files=os.listdir(b['src'])
  for file_name in s_files:
    ff_name = os.path.join(b['src'], file_name)  
    if (os.path.isfile(ff_name) and ff_name.endswith('.json')):
      print ff_name
      target_file_name=os.path.join(b['dest'], file_name)
      BLOCKSIZE = 1048576
      with codecs.open(ff_name, "r", "utf-16-le") as source_file:
        with codecs.open(target_file_name, "w+", "utf-8") as target_file:
          while True:
            contents = source_file.read(BLOCKSIZE)
            if not contents:
              break
            target_file.write(contents)

If I hexdump -C I see:

Wed Jan 11$ hexdump -C svy-m-317.json 
00000000  ef bb bf 7b 0d 0a 20 20  20 20 22 6e 61 6d 65 22  |...{..    "name"|
00000010  3a 22 53 61 76 6f 72 79  20 4d 61 6c 69 62 75 2d  |:"Savory Malibu-|

in the resulting file. How do I remove the BOM?

thx

Solution 1

Just use str.decode and str.encode:

with open(ff_name, 'rb') as source_file:
  with open(target_file_name, 'w+b') as dest_file:
    contents = source_file.read()
    dest_file.write(contents.decode('utf-16').encode('utf-8'))

str.decode will get rid of the BOM for you (and deduce the endianness).

Solution 2

This is the difference between UTF-16LE and UTF-16

• UTF-16LE is little endian without a BOM
• UTF-16 is big or little endian with a BOM

So when you use UTF-16LE, the BOM is just part of the text. Use UTF-16 instead, so the BOM is automatically removed. The reason UTF-16LE and UTF-16BE exist is so people can carry around "properly-encoded" text without BOMs, which does not apply to you.

Note what happens when you encode using one encoding and decode using the other. (UTF-16 automatically detects UTF-16LE sometimes, not always.)

>>> u'Hello, world'.encode('UTF-16LE')
'H\x00e\x00l\x00l\x00o\x00,\x00 \x00w\x00o\x00r\x00l\x00d\x00'
>>> u'Hello, world'.encode('UTF-16')
'\xff\xfeH\x00e\x00l\x00l\x00o\x00,\x00 \x00w\x00o\x00r\x00l\x00d\x00'
 ^^^^^^^^ (BOM)

>>> u'Hello, world'.encode('UTF-16LE').decode('UTF-16')
u'Hello, world'
>>> u'Hello, world'.encode('UTF-16').decode('UTF-16LE')
u'\ufeffHello, world'
    ^^^^ (BOM)

Or you can do this at the shell:

for x in * ; do iconv -f UTF-16 -t UTF-8 <"$x" | dos2unix >"$x.tmp" && mv "$x.tmp" "$x"; done

Comments

[timpone]

cool - works well, do you know how to add a crlf -> lf conversion facility in the read? thx if you can help

[Marcin Kaminski]

That approach (storing the entire file in memory twice) isn't very efficient, if you're working with large files.