Introduction
Twisted is currently being ported to work with Python 3.3. This document covers Twisted-specific issues in porting your code to Python 3.
API Differences
twisted.python.failure
Failure.trap
    raises itself (i.e. a Failure) in Python 2. In Python 3,
    the wrapped exception will be re-raised.
Byte Strings and Text Strings
Several APIs which on Python 2 accepted or produced byte strings
    (instances of str, sometimes just called bytes) have
    changed to accept or produce text strings (instances of str,
    sometimes just called text or unicode) on Python 3.
From twisted.internet.address, the IPv4Address
    and IPv6Address classes have had two attributes change from
    byte strings to text strings: type and host.
twisted.python.log has shifted significantly towards text
    strings from byte strings.  Logging events, particular those produced by a
    call like msg("foo"), must now be text strings.  Consequently,
    on Python 3, event dictionaries passed to log observes will contain text
    strings where they previously contained byte strings.
twisted.python.runtime.platformType and the return value
    from twisted.python.runtime.Platform.getType are now both text
    strings.
twisted.python.filepath.FilePath has not changed.
    It supports only byte strings.  This will probably require applications to
    update their usage of FilePath, at least to pass explicit byte
    string literals rather than "native" string literals (which are text on
    Python 3).
reactor.addSystemEventTrigger arguments that were
    previously byte strings are now native strings.
twisted.names.dns deals with strings with a wide range of
    meanings, often several for each DNS record type.  Most of these strings
    have remained as byte strings, which will probably require application
    updates (for the reason given in the FilePath section above).
    Some strings have changed to text strings, though.  Any string representing
    a human readable address (for
    example, Record_A's address parameter) is now a
    text string.  Additionally, time-to-live (ttl) values given as strings must
    now be given as text strings.
twisted.web.resource.IResource continues to deal with URLs
    and all URL-derived values as byte strings.
twisted.web.resource.ErrorPage has several string attributes
    (template, brief, and detail) which
    were previously byte strings.  On Python 3 only, these must now be text
    strings.