A string subclass that stores an encoding, easing interoperability between byte strings and Unicode strings.

encodedstring.py

"""
Copyright (c) 2012-2014, Eventbrite and Contributors
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"""


class EncodedString(str):
    """A string with a stored encoding.

    By storing the unicode encoding used, we're able to handle unicode decoding
    without falling back to the system default encoding. If constructed any way
    other than with the ``new`` class method, encoding is set to UTF-8.
    """

    encoding = 'utf8'

    @classmethod
    def new(cls, content, encoding='utf8', encode=True):
        """Create a new instance of EncodedString.

        Creates a new EncodedString instance with the given ``encoding``.
        ``content`` will be encoded before instantiation by default.  If
        ``content`` has already been encoded, pass ``False for the ``encode``
        keyword argument.
        """

        if encode:
            content = content.encode(encoding)
        result = cls(content)
        result.encoding = encoding

        return result

    def __add__(self, other):
        """Concatenate EncodedString with another object.

        If ``other`` is a Unicode object, the contents of ``self`` will be
        decoded. Otherwise a new EncodedString will be returned with the same
        encoding.
        """

        if isinstance(other, unicode):
            # decode and concatenate
            return u'%s%s' % (self, other)

        # return a new EncodedString keeping the same encoding
        return EncodedString.new(
            '%s%s' % (self, other),
            self.encoding,
            encode=False,
        )

    def __radd__(self, other):
        """Concatenate EncodedString with another object.

        If ``other`` is a Unicode object, the contents of ``self`` will be
        decoded. Otherwise a new EncodedString will be returned with the same
        encoding.
        """

        if isinstance(other, unicode):
            # decode and concatenate
            return u'%s%s' % (other, self)

        # return a new EncodedString keeping the same encoding
        return EncodedString.new(
            '%s%s' % (other, self),
            self.encoding,
            encode=False,
        )

    def __unicode__(self):
        """Return a unicode representation using the stored encoding."""

        return self.decode()

    def decode(self, *args):
        """Decode EncodedString contents to a Unicode object.

        If no encoding is specified, use the stored encoding.
        """

        # if args are omitted, use the stored encoding
        if len(args) == 0:
            args = [self.encoding]

        return str.decode(self, *args)