string.py 文件源码

def _apply(self, value):
        decoded = super(ByteString, self)._apply(value) # type: Text

        #
        # No need to catch UnicodeEncodeErrors here; UTF-8 can handle
        # any unicode value.
        #
        # Technically, we could get this error if we encounter a code
        # point beyond U+10FFFF (the highest valid code point in the
        # Unicode standard).
        #
        # However, it's not possible to create a `unicode` object with
        # an invalid code point, so we wouldn't even be able to get
        # this far if the incoming value contained a character that
        # can't be represented using UTF-8.
        #
        # Note that in some versions of Python, it is possible (albeit
        # really difficult) to trick Python into creating unicode
        # objects with invalid code points, but it generally requires
        # using specific codecs that aren't UTF-8.
        #
        # Example of exploit and release notes from the Python release
        # (2.7.6) that fixes the issue:
        #
        #   - https://gist.github.com/rspeer/7559750
        #   - https://hg.python.org/cpython/raw-file/99d03261c1ba/Misc/NEWS
        #

        # Normally we return ``None`` if we get any errors, but in this
        # case, we'll let the superclass method decide.
        return decoded if self._has_errors else decoded.encode('utf-8')