Porting to Python 3

  1. Introduction
  2. API Differences
  3. Byte Strings and Text Strings


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


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.


Version: 12.3.0