That's because std::string does not carry any sort of encoding information, std::string is basically a wrapper around bytes (hopefully I'm not misreading this, I'm far from an expert C/C++ programmer). Due to this, python can't make any assumptions about encoding/decoding without the possibility of getting it wrong.
"Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8), all members of this class (such as length or size), as well as its iterators, will still operate in terms of bytes (not actual encoded characters)."
"Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8), all members of this class (such as length or size), as well as its iterators, will still operate in terms of bytes (not actual encoded characters)."
https://stackoverflow.com/questions/1010783/what-encoding-do...
http://www.cplusplus.com/reference/string/string/