a sequence of code points, immutable

Python keep characters as unicode in memory

String read from a file is byte string, need to be decoded to unicode

Output unicode to a file, need to encode to byte string

Print a unicode on console, it is encoded to byte string automatically by default encoding method

ord, convert a string to its unicode code point

unichr, convert an integer into a Unicode string

type 'str' represents byte string in Python 2, type 'unicode' represent unicode

type 'str' represents unicode in Python 3, type 'bytes' represent byte string