What’s New In Python 3.4
This article explains the new features in Python 3.4, compared to 3.3.
For full details, see the
Prerelease users should be aware that this document is currently in
draft form. It will be updated substantially as Python 3.4 moves towards
release, so it’s worth checking back even after reading earlier versions.
Summary – Release highlights
New syntax features:
New library modules:
New built-in features:
Significantly Improved Library Modules:
- SHA-3 (Keccak) support for hashlib.
- TLSv1.1 and TLSv1.2 support for ssl.
Please read on for a comprehensive list of user-facing changes.
Other Language Changes
Some smaller changes made to the core Python language are:
- Unicode database updated to UCD version 6.2.
- Import now raises the new exception ModuleNotFoundError (subclass of
ImportError) when it cannot find something.
The dis module is now built around an Instruction class that
provides details of individual bytecode operations and a
get_instructions() iterator that emits the Instruction stream for a
given piece of Python code. The various display tools in the dis
module have been updated to be based on these new components.
The new dis.Bytecode class provides an object-oriented API for
inspecting bytecode, both in human-readable form and for iterating over
(Contributed by Nick Coghlan, Ryan Kelly and Thomas Kluyver in issue 11816)
Added FAIL_FAST flag to halt test running as soon as the first failure is
detected. (Contributed by R. David Murray and Daniel Urban in issue 16522.)
SMTPException is now a subclass of OSError, which allows
both socket level errors and SMTP protocol level errors to be caught in one
try/except statement by code that only cares whether or not an error occurred.
The getparams() method now returns a namedtuple rather than a
plain tuple. (Contributed by Claudiu Popa in issue 17487.)
Major performance enhancements have been added:
- The UTF-32 decoder is now 3x to 4x faster.
Build and C API Changes
Changes to Python’s build process and to the C API include:
Unsupported Operating Systems
Deprecated Python modules, functions and methods
Deprecated functions and types of the C API
Porting to Python 3.4
This section lists previously described changes and other bugfixes
that may require changes to your code.
- The ABCs defined in importlib.abc now either raise the appropriate
exception or return a default value instead of raising
NotImplementedError blindly. This will only affect code calling
super() and falling through all the way to the ABCs. For compatibility,
catch both NotImplementedError or the appropriate exception as needed.
- The module type now initializes the __package__ and __loader__
attributes to None by default. To determine if these attributes were set
in a backwards-compatible fashion, use e.g.
getattr(module, '__loader__', None) is not None.
- importlib.util.module_for_loader() now sets __loader__ and
__package__ unconditionally to properly support reloading. If this is not
desired then you will need to set these attributes manually. You can use
importlib.util.module_to_load() for module management.
- Import now resets relevant attributes (e.g. __name__, __loader__,
__package__, __file__, __cached__) unconditionally when reloading.
- Frozen packages no longer set __path__ to a list containg the package name
but an empty list instead. Determing if a module is a package should be done
using hasattr(module, '__path__').
- PyErr_SetImportError() now sets TypeError when its msg
argument is not set. Previously only NULL was returned.
- py_compile.compile() now raises FileExistsError if the file path
it would write to is a symlink or a non-regular file. This is to act as a
warning that import will overwrite those files with a regular file regardless
of what type of file path they were originally.
- importlib.abc.SourceLoader.get_source() no longer raises
ImportError when the source code being loaded triggers a
SyntaxError or UnicodeDecodeError. As ImportError is
meant to be raised only when source code cannot be found but it should, it was
felt to be over-reaching/overloading of that meaning when the source code is
found but improperly structured. If you were catching ImportError before and
wish to continue to ignore syntax or decoding issues, catch all three