Python: the coolest is yet to come

{ The COOLEST is yet TO COME “event”:
“PDI DEVCON 2013” “author”: “Pablo Enfedaque” “twi5er”: “pablitoev56”

{ “event”: “PDI DEVCON 2013”, “author”: “Pablo Enfedaque”, “twi5er”: “pablitoev56”}
>  Today we are going to see a quick tour through Python’s newest features >  The new super function >  The yield from statement >  The new exception chaining >  Single-‐‑dispatch generic functions >  Python virtual environments >  The enum module >  The asyncio module >  And lots of other new features Welcome!

The super function

Let’s implement a SilentDict class SilentDict(dict): def __getitem__(self, key): """Called to implement evaluation of self[key] :returns: None by default """ try: return super(SilentDict, self).__getitem__(key) except KeyError: return None >>> d = SilentDict() >>> print (d[“a”]) None >>> d = SilentDict({"a": 1, "b": 2}) >>> print(d["a"]) 1 >>> print(d["a"]) None

Let’s implement a SilentDict class SilentDict(dict): def __getitem__(self, key): """Called to implement evaluation of self[key] :returns: None by default """ try: return super().__getitem__(key) except KeyError: return None >>> d = SilentDict() >>> print (d[“a”]) None >>> d = SilentDict({"a": 1, "b": 2}) >>> print(d["a"]) 1 >>> print(d["a"]) None

>  h5p://docs.python.org/3/library/ functions.html#super >  PEP 3135: New Super >  h5p://www.python.org/dev/peps/pep-‐‑3135/ >  Introduced in Python 3.0 >  Standard Library updated to use it >  No oﬃcial backport The super function

The yield from statement

Let’s implement itertools.chain

Let’s implement itertools.chain def chain(*iterables): # chain('ABC', 'DEF') --> A B C D E F for it in iterables: yield from it >>> list(chain('ABC', 'DEF')) ['A', 'B', 'C', 'D', 'E', 'F'] >>> list(chain([1, 2, 3], (4, 5, 6), [7, 8, 9])) [1, 2, 3, 4, 5, 6, 7, 8, 9]

>  PEP 380: Syntax for Delegating to a Subgenerator >  h5p://www.python.org/dev/peps/pep-‐‑0380/ >  Introduced in Python 3.3 >  No backport The yield from statement

The new exception chaining

The new exception chaining from urllib.request import urlopen from urllib.error import URLError class CustomException(Exception): """Out custom exception for this example""” def requester(url): """Open and read given url""" try: return urlopen(url).readall() except URLError: raise CustomException def call_the_requester(url): return requester(url) def main_app(url): print(call_the_requester(url)) if __name__ == "__main__": main_app("http://unknown_host:8765")

The new exception chaining $ python3.4 raise_from_none_examples.py Traceback (most recent call last): ... File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/urllib/ request.py", line 1255, in do_open raise URLError(err) urllib.error.URLError: <urlopen error [Errno 8] nodename nor servname provided, or not known> During handling of the above exception, another exception occurred: Traceback (most recent call last): File "raise_from_none_examples.py", line 39, in <module> main_app("http://unknown_host:8765") File "raise_from_none_examples.py", line 35, in main_app print(call_the_requester(url)) File "raise_from_none_examples.py", line 31, in call_the_requester return requester(url) File "raise_from_none_examples.py", line 27, in requester raise CustomException __main__.CustomException

The new exception chaining from urllib.request import urlopen from urllib.error import URLError class CustomException(Exception): """Out custom exception for this example""” def requester(url): """Open and read given url""" try: return urlopen(url).readall() except URLError as exc: raise CustomException from exc def call_the_requester(url): return requester(url) def main_app(url): print(call_the_requester(url)) if __name__ == "__main__": main_app("http://unknown_host:8765")

The new exception chaining $ python3.4 raise_from_none_examples.py Traceback (most recent call last): ... File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/ request.py", line 1242, in do_open raise URLError(err) urllib.error.URLError: <urlopen error [Errno 8] nodename nor servname provided, or not known> The above exception was the direct cause of the following exception: Traceback (most recent call last): File "raise_from_none_examples.py", line 40, in <module> main_app("http://unknown_host:8765") File "raise_from_none_examples.py", line 36, in main_app print(call_the_requester(url)) File "raise_from_none_examples.py", line 32, in call_the_requester return requester(url) File "raise_from_none_examples.py", line 28, in requester raise CustomException from exc __main__.CustomException

The new exception chaining from urllib.request import urlopen from urllib.error import URLError class CustomException(Exception): """Out custom exception for this example""” def requester(url): """Open and read given url""" try: return urlopen(url).readall() except URLError: raise CustomException from None def call_the_requester(url): return requester(url) def main_app(url): print(call_the_requester(url)) if __name__ == "__main__": main_app("http://unknown_host:8765")

The new exception chaining $ python3.4 raise_from_none_examples.py Traceback (most recent call last): File "raise_from_none_examples.py", line 40, in <module> main_app("http://unknown_host:8765") File "raise_from_none_examples.py", line 36, in main_app print(call_the_requester(url)) File "raise_from_none_examples.py", line 32, in call_the_requester return requester(url) File "raise_from_none_examples.py", line 28, in requester raise CustomException from None __main__.CustomException

>  Several PEPs involved: >  PEP 3134: Exception Chaining and Embedded Tracebacks >  h5p://www.python.org/dev/peps/pep-‐‑3134 >  PEP 409: Suppressing exception context >  h5p://www.python.org/dev/peps/pep-‐‑0409/ >  PEP 415: Implement context suppression with exception a5ributes >  h5p://www.python.org/dev/peps/pep-‐‑0415 >  Introduced in Python 3.0 and 3.3 >  No oﬃcial backport The new exception chaining

Single-‐‑dispatch generic functions

Let’s create some animals class Duck: def quack(self): print("quack") class Cat: def meow(self): print("meow") class Dog: def bark(self): print("bark”) class Cow: def moo(self): print("moo") donald = Duck() garfield = Cat() milu = Dog() milka = Cow()

Let’s play animals’ sounds def make_sound(animal): if isinstance(animal, Duck): animal.quack() elif isinstance(animal, Cat): animal.meow() elif isinstance(animal, Dog): animal.bark() else: raise NotImplementedError("Unknown animal") >>> make_sound(donald) quack >>> make_sound(garfield) meow >>> make_sound(milu) bark >>> make_sound(milka) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 11, in make_sound NotImplementedError: Unknown animal

Single-‐‑dispatch generic functions import functools @functools.singledispatch def make_sound(animal): raise NotImplementedError("Unknown animal") @make_sound.register(Duck) def make_duck_sound(animal): animal.quack() @make_sound.register(Cat) def make_cat_sound(animal): animal.meow() @make_sound.register(Dog) def _(animal): animal.bark()

Single-‐‑dispatch generic functions >>> make_sound(donald) quack >>> make_sound(garfield) meow >>> make_sound(milu) bark >>> make_sound(milka) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Library/Frameworks/Python.framework/Versions/3.4/lib/ python3.4/functools.py", line 632, in wrapper return dispatch(args[0].__class__)(*args, **kw) File "<stdin>", line 5, in make_sound NotImplementedError: Unknown animal

>  h5p://docs.python.org/dev/library/ functools.html#functools.singledispatch >  PEP 443: Single-‐‑dispatch generic functions >  h5p://www.python.org/dev/peps/pep-‐‑0443/ >  Introduced in Python 3.4 >  No oﬃcial backport Single-‐‑dispatch generic functions

Python virtual environments

Python virtual environments $ pyvenv /tmp/test_venv $ ls /tmp/test_venv/ bin include lib pyvenv.cfg $ ls /tmp/test_venv/bin/ activate activate.csh activate.fish python python3 python3.4 $ cat /tmp/test_venv/pyvenv.cfg home = /Library/Frameworks/Python.framework/Versions/3.4/bin include-system-site-packages = false version = 3.4.0 $ pyvenv /tmp/test_venv --symlinks --clear --system-site-packages $ cat /tmp/test_venv/pyvenv.cfg home = /Library/Frameworks/Python.framework/Versions/3.4/bin include-system-site-packages = true version = 3.4.0 $ ls -lAhtr /tmp/test_venv/bin/python3.4 lrwxr-xr-x 1 pev wheel 63B 5 nov 00:21 /tmp/test_venv/bin/python3.4 -> / Library/Frameworks/Python.framework/Versions/3.4/bin/python3.4

Python virtual environments $ source /tmp/test_venv/bin/activate (test_venv) ...$ which python /tmp/test_venv/bin/python (test_venv) ...$ which python3.4 /tmp/test_venv/bin/python3.4 (test_venv) ...$ python Python 3.4.0a4 (v3.4.0a4:e245b0d7209b, Oct 20 2013, 02:43:50) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> sys.prefix, sys.base_prefix ('/private/tmp/test_venv', '/Library/Frameworks/Python.framework/Versions/3.4') >>> sys.exec_prefix, sys.base_exec_prefix ('/private/tmp/test_venv', '/Library/Frameworks/Python.framework/Versions/3.4') (test_venv) ...$ deactivate $ which python /usr/bin/python

>  Features >  Supports symbolic links (recommended) >  Access both environment and system site-‐‑packages >  pyvenv.cfg environment configuration file: >  home: path to original Python installation bin >  include-‐‑system-‐‑site-‐‑packages: access system site-‐‑packages after the environment site-‐‑packages >  version: Python version in use >  Public API to let 3rd party virtual environments customise the environment creation >  Subclass EnvBuilder and redefine desired methods Python virtual environments

>  h5p://docs.python.org/3/library/venv.html >  PEP 405: Python Virtual Environments >  h5p://www.python.org/dev/peps/pep-‐‑0405/ >  Introduced in Python 3.3 >  No oﬃcial backport, although quite similar to virtualenv Python virtual environments

The enum module

Let’s implement a traﬃc light RED, ORANGE, GREEN = range(3) # Colors STOPPED, RUNNING = range(2) # Statuses class TrafficLight: def __init__(self, light_color, status): assert light_color in (RED, ORANGE, GREEN), "Not a valid color" assert status in (RUNNING, STOPPED), "Not a valid status" self.color = light_color self.status = status def print_state(self): color_name = "red" if self.color == RED else "green" if self.color == GREEN else "orange" status_name = "running" if self.status == RUNNING else "stopped" print("Traffic light is {} in color {}".format(status_name, color_name)) >>> my_semaphore = TrafficLight(RUNNING, RED) >>> my_semaphore.print_state() Traffic light is stopped in color orange

Let’s implement a traﬃc light RED, ORANGE, GREEN = range(3) # Colors STOPPED, RUNNING = range(2) # Statuses class TrafficLight: def __init__(self, light_color, status): assert light_color in (RED, ORANGE, GREEN), "Not a valid color" assert status in (RUNNING, STOPPED), "Not a valid status" self.color = light_color self.status = status def print_state(self): color_name = "red" if self.color == RED else "green" if self.color == GREEN else "orange" status_name = "running" if self.status == RUNNING else "stopped" print("Traffic light is {} in color {}".format(status_name, color_name)) >>> STOPPED is RED and RUNNING is ORANGE True >>> (RUNNING + ORANGE) * GREEN 4

Introducing the enum module from enum import Enum Color = Enum("Color", "red orange green") # Colors Status = Enum("Status", "stopped running") # Statuses class TrafficLight: def __init__(self, light_color, status): assert light_color in Color, "Not a valid color" assert status in Status, "Not a valid status" self.color = light_color self.status = status def print_state(self): color_name = "red" if self.color == Color.red else "green" if self.color == Color.green else "orange" status_name = "running" if self.status == Status.running else "stopped" print("Traffic light is {} in color {}".format(status_name, color_name)) my_semaphore = TrafficLight(Status.running, Color.red)

Introducing the enum module >>> my_semaphore = TrafficLight(Status.running, Color.red) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 3, in __init__ AssertionError: Not a valid color >>> my_semaphore = TrafficLight(Color.red, Status.running) >>> my_semaphore.print_state() Traffic light is running in color red >>> Status.stopped is Color.red False >>> Status.running is Color.orange False >>> (Status.running + Color.orange) * Color.green Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'Status' and 'Color'

More about enum module class Color(Enum): # enumaration red = 0 orange = 10 # enumeration members green = 20 # custom non-consecutive values ruby = 0 # aliases >>> print(Color.green) Color.green >>> print(repr(Color.green)) <Color.green: 20> >>> print(repr(Color.ruby)) # this is an alias <Color.red: 0> >>> print(Color.orange.name) # we can retrieve a member name orange >>> print(Color["orange"]) # we can get the enum member from its name Color.orange >>> print(Color.orange.value) # we can retrieve a member value 10 >>> print(Color(10)) # we can get the enum member from its value Color.orange

More about enum module class Color(Enum): red = 0 orange = 10 green = 20 class Status(Enum): running = 0 stopped = 1 class TrafficLight: def __init__(self, light_color, status): assert light_color in Color, "Not a valid color" assert status in Status, "Not a valid status" self.color = light_color self.status = status def print_state(self): print("Traffic light is {} in color {}".format(self.status.name, self.color.name)) >>> my_semaphore = TrafficLight(Color.red, Status.running) >>> my_semaphore.print_state() Traffic light is running in color red

>  And still more features >  Iteration over enumeration members >  Ordered dictionary __members__ special a5ribute >  Define methods and class methods >  Even redefine __str__ or __repr__ >  IntEnum to preserve old int behaviour >  @enum.unique to enforce no aliases are defined >  Possibility to define other custom Enum sublcasses >  Functional API More about enum module

>  h5p://docs.python.org/3.4/library/enum.html >  PEP 435: Adding an Enum type to the Python standard library >  h5p://www.python.org/dev/peps/pep-‐‑0435/ >  Introduced in Python 3.4 >  Standard Library updated to use enums >  IntEnum when backwards-‐‑compatibility broken >  Enum in new developments and internal modules >  Oﬃcial backport available in PyPi >  h5ps://pypi.python.org/pypi/enum34/ The enum module

The asyncio module

>  Python’s asynchronous IO Support Rebooted >  No new language features, no new lib extensions >  Based on a customisable event loop >  Interface to manage the event loop and its policies >  Interface to implement or adapt event loops >  Diﬀerent 3rd party async frameworks could interoperate >  Coroutines, futures and tasks >  Transports and protocols >  Use yield from to delegate or callbacks The asyncio module (aka. Tulip)

>  h5p://docs.python.org/3.4/library/enum.html >  PEP 3156: Asynchronous IO Support Rebooted: the "ʺasyncio"ʺ Module >  h5p://www.python.org/dev/peps/pep-‐‑3156/ >  Reference implementation in Python 3.4 >  Expected ﬁnal status in Python 3.5 >  Backport to 3.3 available in PyPi >  h5ps://pypi.python.org/pypi/asyncio/0.1.1 The asyncio module

>  unicode, unicode everywhere >  generators, generators everywhere >  or iterators >  uniNest.mock (port of Michael Foord’s mock) >  contextlib.ExitStack and contextlib.ContextDecorator >  Be5er GIL (but still Global Interpreter Lock) >  concurrent.futures for async computation >  Qualiﬁed name for classes and functions >  selectors module >  … And still lots of new features

Q&A

Q&A Are we done yet?

>  Not yet >  Only 22 slides missing >  16 only with pictures, and even 1 animated GIF >  Sorry, no ki5ens Q&A Are we done yet?

Q&A Should we move now to Python 3?

>  YES >  Well, maybe NO >  Well, let me explain Q&A Should we move now to Python 3?

h5p://www.python.org/download/releases/2.7/ Release schedule: >  … >  2.7.0 ﬁnal: July 3, 2010 >  … >  2.7.6 candidate 1: October 26, 2013 >  ??? >  2.7.X end of support: ≈ 2016 Python 2.7

h5p://www.python.org/download/releases/3.4.0/ Release schedule: >  3.4.0 alpha 4: October 20, 2013 >  3.4.0 beta 1 (feature freeze): November 24, 2013 >  3.4.0 beta 2: January 5, 2014 >  3.4.0 candidate 1: January 19, 2014 >  3.4.0 candidate 2: February 2, 2014 >  3.4.0 ﬁnal: February 23, 2014 Python 3.4

The long journey to Python 3

Meanwhile, most of the community

>  Great features are waiting us in Python 3 >  We are beyond half the planned life of Python 2.7 >  Python 2.6 is oﬃcially retired with 2.6.9 release >  Most 3rd party dependencies already in Python 3 >  Or we could return to OSS all that we have been given >  Porting to Python 3 is not such a big deal >  In most of the cases >  So, no more excuses >  It’s time to start moving to Python 3 Conclusions

Conclusions

Q&A Thanks for coming! Slides: h5p://goo.gl/Yrzt0Q Code: h5p://goo.gl/V9bv72

Python: the coolest is yet to come

Python: the coolest is yet to come

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