Async method for randomly splitting users into groups

CASE  
     WHEN MOD(CAST(CONCAT("0x", SUBSTRING(TO_HEX(SHA1(user_id)),-4)) AS INT64), 10) IN (0, 1, 2, 3)  
     THEN "A"  
     WHEN MOD(CAST(CONCAT("0x", SUBSTRING(TO_HEX(SHA1(user_id)),-4)) AS INT64), 10) IN (4, 5, 6, 7)  
     THEN "B"
     WHEN MOD(CAST(CONCAT("0x", SUBSTRING(TO_HEX(SHA1(user_id)),-4)) AS INT64), 10) IN (8, 9)  
     THEN "C"
END AS user_group

import hashlib
def assign_user_group(user_id):  
    # Convert user_id to SHA1, then to hexadecimal  
    sha1_hex = hashlib.sha1(user_id.encode()).hexdigest()# Extract the last 4 characters of the hex representation
    last_four_hex = sha1_hex[-4:]

    # Convert the hexadecimal (with "0x" prefix) to an integer and find the modulus 10
    mod_result = int(last_four_hex, 16) % 10

    # Assign user_group based on the mod_result
    if mod_result in [0, 1, 2, 3]:
        user_group = "A"
    elif mod_result in [4, 5, 6, 7]:
        user_group = "B"
    elif mod_result in [8, 9]:
        user_group = "C"
    else:
        # Just in case of unexpected result, not necessary unless mod_result might not be in 0-9
        user_group = "unknown"

    return user_group