python - Warning raised by inserting 4-byte unicode to mysql

Question

Look at the following:

/home/kinka/workspace/py/tutorial/tutorial/pipelines.py:33: Warning: Incorrect string 
value: 'xF0x9Fx91x8AxF0x9F...' for column 't_content' at row 1
n = self.cursor.execute(self.sql, (item['topic'], item['url'], item['content']))

The string 'xF0x9Fx91x8A, actually is a 4-byte unicode: u'U0001f62a'. The mysql's character-set is utf-8 but inserting 4-byte unicode it will truncate the inserted string. I googled for such a problem and found that mysql under 5.5.3 don't support 4-byte unicode, and unfortunately mine is 5.5.224. I don't want to upgrade the mysql server, so I just want to filter the 4-byte unicode in python, I tried to use regular expression but failed. So, any help?

Answer 1

If MySQL cannot handle UTF-8 codes of 4 bytes or more then you'll have to filter out all unicode characters over codepoint U00010000; UTF-8 encodes codepoints below that threshold in 3 bytes or fewer.

You could use a regular expression for that:

>>> import re
>>> highpoints = re.compile(u'[U00010000-U0010ffff]')
>>> example = u'Some example text with a sleepy face: U0001f62a'
>>> highpoints.sub(u'', example)
u'Some example text with a sleepy face: '

Alternatively, you could use the .translate() function with a mapping table that only contains None values:

>>> nohigh = { i: None for i in xrange(0x10000, 0x110000) }
>>> example.translate(nohigh)
u'Some example text with a sleepy face: '

However, creating the translation table will eat a lot of memory and take some time to generate; it is probably not worth your effort as the regular expression approach is more efficient.

This all presumes you are using a UCS-4 compiled python. If your python was compiled with UCS-2 support then you can only use codepoints up to 'U0000ffff' in regular expressions and you'll never run into this problem in the first place.

I note that as of MySQL 5.5.3 the newly-added utf8mb4 codec does supports the full Unicode range.