Tauthon

Tauthon is a backwards-compatible fork of the Python 2.7.18 interpreter with new syntax, builtins, and libraries backported from Python 3.x. Python code and C-extensions targeting Python 2.7 or below are expected to run unmodified on Tauthon and produce the same output. But with Tauthon, that code can now use some of the new features from Python 3.x.

Virtualenv support is provided by an external plugin: virtualenv-tauthon.

What's new in Tauthon

Function Annotations

>>> def f(a:int, b:str) -> list:
...     pass
...
>>> f.__annotations__
{'a': <type 'int'>, 'b': <type 'str'>, 'return': <type 'list'>}

More info: PEP 3107

Keyword-Only Arguments

>>> def f(a, *, b):
...     pass
...
>>> f(1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes exactly 1 positional argument (2 given)
>>> f(1, b=2)
>>>

More info: PEP 3102

"async" and "await" Syntax

>>> import types
>>> @types.coroutine
... def delayed_print():
...     printme = yield
...     print printme
...
>>> async def main():
...     while True:
...         await delayed_print()
...
>>> coro = main()
>>> coro.send(None)
>>> coro.send("hello")
hello
>>> coro.send("there")
there
>>> coro.send("friend")
friend

More info: PEP 492, Tutorial

Argument-less "super"

>>> class MyList(list):
...     def __repr__(self):
...             return "MyList" + super().__repr__()
...
>>> MyList(range(3))
MyList[0, 1, 2]

More info: PEP 3135, API Docs

New Metaclass Syntax

>>> from collections import OrderedDict
>>> class Meta(type):
...     @staticmethod
...     def __prepare__(name, bases, **kwds):
...             return OrderedDict()
...     def __new__(cls, name, bases, namespace, **kwds):
...             namespace.update(kwds)
...             res = type.__new__(cls, name, bases, dict(namespace))
...             res._namespace = namespace
...             return res
...     def __init__(*args, **kwds):
...             pass
...
>>> class MyClass(metaclass=Meta, foo="bar"):
...     def first(self): pass
...     def second(self): pass
...     def third(self): pass
...
>>> MyClass.foo
'bar'
>>> MyClass._namespace
OrderedDict([('__module__', '__main__'), ('first', <function first at 0x1007ef568>), ('second', <function second at 0x10131b060>), ('third', <function third at 0x10131b118>), ('foo', 'bar')])

More info: PEP 3115, Introduction to Metaclasses (in Python 2.x), API Docs (Python 3.x)

"nonlocal"

>>> x = 0
>>> def f():
...     x = 1
...     def g():
...         nonlocal x
...         x = 2
...     print x
...     g()
...     print x
...
>>> print x; f(); print x
0
1
2
0
>>> nonlocal = True; print nonlocal
True

Caveat: As you can see, to maintain backwards compatibility nonlocal is not a keyword, unlike in Python 3.x. So it can still be used as an identifier.

More info: PEP 3104, API Docs

"yield from" Syntax

>>> def generator():
...     yield from range(3)
...     yield from ['a', 'b', 'c']
...
>>> [x for x in generator()]
[0, 1, 2, 'a', 'b', 'c']

More info: PEP 380

"typing" Module

>>> from typing import List, Dict
>>> List[Dict[str, int]]
typing.List[typing.Dict[str, int]]
>>> def wordcount(words:List[str]) -> Dict[str, int]:
...     return collections.Counter(words)

More info: PEP 483, PEP 484, API Docs

Function Signatures in "inspect"

>>> import inspect
>>> def f(a:int, b, *args, c:str="foo", **kwds) -> list: pass
...
>>> inspect.signature(f)
<Signature (a:int, b, *args, c:str='foo', **kwds) -> list>
>>> inspect.signature(f).parameters['c'].default
'foo'

More info: PEP 362, API Docs

Matrix Multiplication Operator

>>> import numpy as np
>>> class Matrix(np.matrix):
...     def __matmul__(self, other):
...         return np.dot(self, other)
...
>>> X = Matrix([[1, 2], [3, 4]])
>>> Y = Matrix([[4, 3], [2, 1]])
>>> print X
[[1 2]
 [3 4]]
>>> print Y
[[4 3]
 [2 1]]
>>> print X @ Y
[[ 8  5]
 [20 13]]
>>> X @= Y
>>> X
matrix([[ 8,  5],
        [20, 13]])

More info: PEP 465

Fine-grained OSErrors
```
>>> open("not a file")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'not a file'
>>> try:
...     open("not a file")
... except FileNotFoundError:
...     pass
...
>>>
```
Caveat: As you can see from the example, to maintain full backwards compatibility Tauthon does not raise these new OSErrors. Rather it gives you fine-grained OSErrors that you can catch them with, as an alternative to checking errno.

More info: PEP 3151, API Docs

Underscores in Numeric Literals

>>> 1_234_567
1234567
>>> 0xBEEF_CAFE
3203386110
>>> 0b1111_0000
240
>>>

More info: PEP 515

"concurrent.futures" Module

>>> from concurrent.futures import ThreadPoolExecutor
>>> from datetime import datetime
>>> import time
>>> def snooze(seconds):
...     print "It's now %s, snoozing for %d seconds." % (datetime.now(), seconds)
...     time.sleep(seconds)
...     print "BEEP BEEP BEEP it's %s, time to get up!" % datetime.now()
...
>>> def snooze_again(future):
...     print "Going back to sleep"
...     snooze(3)
...
>>> pool = ThreadPoolExecutor()
>>> future = pool.submit(snooze, 60)
It's now 2016-11-17 12:09:41.822658, snoozing for 60 seconds.
>>> print future
<Future at 0x1040b7b10 state=running>
>>> future.add_done_callback(snooze_again)
>>> print datetime.now()
2016-11-17 12:10:11.189143
>>> BEEP BEEP BEEP it's 2016-11-17 12:10:41.824054, time to get up!
Going back to sleep
It's now 2016-11-17 12:10:41.824206, snoozing for 3 seconds.
BEEP BEEP BEEP it's 2016-11-17 12:10:44.829196, time to get up!

More info: PEP 3148, API Docs

"types.MappingProxyType"

>>> import types
>>> original = {'a': 1}
>>> read_only_view = types.MappingProxyType(original)
>>> read_only_view['a']
1
>>> read_only_view['b'] = 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'dict_proxy' object does not support item assignment
>>> original['c'] = 3
>>> original
{'a': 1, 'c': 3}
>>> read_only_view['c']
3

More info: API Docs

"selectors" Module
```
>>> import selectors
```
More info: API Docs
UTF-8 as the default source encoding

More info: PEP 3120
monotonic time, performance counter, and process time functions

More info: PEP 418
tab completion enabled by default in the interactive interpreter

More info: BPO 5845
module/function aliases and wrappers matching Python3's module renaming and reorganization

More info: PR #128

Building and Installation

Linux:

$ ./configure
$ make

OSX:

$ brew install openssl xz
$ CPPFLAGS="-I$(brew --prefix openssl)/include" LDFLAGS="-L$(brew --prefix openssl)/lib" MACOSX_DEPLOYMENT_TARGET=10.6 ./configure
$ make

You can then run Tauthon with ./tauthon or ./tauthon.exe.

Install with

$ make install

Backwards-incompatibilities

There are a small handful of backwards incompatibilities introduced by Tauthon. Triggering these involves checking the Python version, introspection of Python internals (including the AST), or depending on errors being raised from nonexistent new features.

License

Tauthon is licensed under the Python Software License, (see the LICENSE file for details). This is not an official Python release; see PEP 404.

naftaliharris/tauthon