Python: Find equivalent surrogate pair from non-BMP unicode char

Question

The answer presented here: How to work with surrogate pairs in Python? tells you how to convert a surrogate pair, such as '\ud83d\ude4f' into a single non-BMP unicode character (the answer being "\ud83d\ude4f".encode('utf-16', 'surrogatepass').decode('utf-16')). I would like to know how to do this in reverse. How can I, using Python, find the equivalent surrogate pair from a non-BMP character, converting '\U0001f64f' (🙏) back to '\ud83d\ude4f'. I couldn't find a clear answer to that.

Answer 1

You'll have to manually replace each non-BMP point with the surrogate pair. You could do this with a regular expression:

import re

_nonbmp = re.compile(r'[\U00010000-\U0010FFFF]')

def _surrogatepair(match):
    char = match.group()
    assert ord(char) > 0xffff
    encoded = char.encode('utf-16-le')
    return (
        chr(int.from_bytes(encoded[:2], 'little')) + 
        chr(int.from_bytes(encoded[2:], 'little')))

def with_surrogates(text):
    return _nonbmp.sub(_surrogatepair, text)

Demo:

>>> with_surrogates('\U0001f64f')
'\ud83d\ude4f'

Answer 2

It's a little complex, but here's a one-liner to convert a single character:

>>> emoji = '\U0001f64f'
>>> ''.join(chr(x) for x in struct.unpack('>2H', emoji.encode('utf-16be')))
'\ud83d\ude4f'

To convert a mix of characters requires surrounding that expression with another:

>>> emoji_str = 'Here is a non-BMP character: \U0001f64f'
>>> ''.join(c if c <= '\uffff' else ''.join(chr(x) for x in struct.unpack('>2H', c.encode('utf-16be'))) for c in emoji_str)
'Here is a non-BMP character: \ud83d\ude4f'