https://bugs.python.org/review/20699/diff/13586/Doc/library/io.rst File Doc/library/io.rst (right): https://bugs.python.org/review/20699/diff/13586/Doc/library/io.rst#newcode23... Doc/library/io.rst:233: :class:`bytearray` is required. Text I/O classes work with Actually writable bytes-like object is required. https://bugs.python.org/review/20699/diff/13586/Doc/library/io.rst#newcode40... Doc/library/io.rst:403: be less than ``len(b)``, depending on specifics of the underlying raw For general bytes-like object len(b) is not the number of bytes. https://bugs.python.org/review/20699/diff/13586/Doc/library/io.rst#newcode50... Doc/library/io.rst:501: return the number of bytes written (never less than ``len(b)``, since if As above. https://bugs.python.org/review/20699/