def SUB_STR_BYTES(string, index, length):
return {'<STR_LIT>': [string, index, length]}<EOL>
Returns the substring of a string.
The substring starts with the character at the specified UTF-8 byte index (zero-based) in the string
and continues for the number of bytes specified.
https://docs.mongodb.com/manual/reference/operator/aggregation/substrBytes/
for more details
:param string: The string or expression of string
:param index: Indicates the starting point of the substring.
:param length: Can be any valid expression as long as it resolves to a non-negative integer or number
:return: Aggregation operator