What's New in Pythons 3.5 and 3.6?
Viacheslav Kakovskyi
Austin Python Meetup 2017
my favourite features

Me!
@kakovskyi
Backend Software Technical Lead
Python 2 and Twisted → Python 3 and asyncio
Share knowledge at Python events
● PyCon Ukraine 2016
● PyCon Poland 2016
● KyivPy 2015, WebCamp Ukraine 2016
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Agenda
1. Syntax changes
2. Library modules
3. Built-in features
4. CPython improvements
5. Standard library improvements
6. Summary
7. Further reading
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Who uses Python 3 in production?
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Who uses Python 3 in production?
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Syntax changes
PEP 492 - coroutines with async and await syntax
● async expression used to define coroutine functions
● await is used to suspend coroutine execution until result is
available
● implement object.__await__(self) to make your object
awaitable
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Python 3.5
async def http_handler():
users = await get_users_from_db()
return '<h1>Online users {}</h1>'.format(len(users))

Syntax changes
PEP 448 - additional unpacking generalizations
● * expression used as iterable unpacking operator
● and ** as dictionary unpacking operator
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Python 3.5
>>> print(*[1], *{2}, 3)
1 2 3
>>> print({'x': 4, **{'y': 5}})
{'x': 4, 'y': 5}

Syntax changes
PEP 515 - underscores in numeric literals
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Python 3.6
>>> 100_500_000
100500000
>>> 0x_DE_AD_BE_AF
3735928495
>>> '{:_}'1.format(100500000)
100_500_000
>>> '{:_x}'1.format(3735928495)
0x_DE_AD_BE_AF

Syntax changes
PEP 530 - asynchronous comprehensions
● Now it's possible to use async for in list, set, dict
comprehensions and generator expressions
● await and can be used inside the expressions
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Python 3.6
result = [await fun() for fun in funcs if await condition()]

Library modules
typing - support of type hints for static code analysis only for
functions
PEP 526 - add support of type annotation for variables (Py3.6)
● Any, Awaitable Callable, Collection, Coroutine,
● Dict, FrozenSet, Generator, Iterable, Iterator
● List, NewType, Set, Tuple
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Python 3.5
def greeting(name: str) -> str:
return 'Hello, {}'.format(name)

Built-in features
PEP-461 - percent formatting support for bytes and bytearray
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Python 3.5
>>> b'Hello, %b' % b'Austin!'
b'Hello, Austin!'

Built-in features
RecursionError is raised when max recursion depth is reached
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Python 3.5
def recursion(level):
# do something awesome
return recursion(level+1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in a
File "<stdin>", line 2, in a
File "<stdin>", line 2, in a
[Previous line repeated 995 more times]
RecursionError: maximum recursion depth exceeded

CPython improvements
PEP-488 Elimination of PYO files
● .pyo files are never used
● .pyc files are used with explicit declaration of optimization
level in filename
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Python 3.5
'{name}.{cache_tag}.opt-{optimization}.pyc'.format(name=module_name,
cache_tag=sys.implementation.cache_tag,
optimization=str(sys.flags.optimize))

CPython improvements
Compact and ordered dict improvement
● Memory usage is 20% less compared to Python 3.5
● dict preserves order of insertion now
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Python 3.6
>>> d = {}
>>> d['a'] = 1
>>> d['b'] = 2
>>> d['c'] = 3
>>> d
{'a': 1, 'b': 2, 'c': 3}

PEP-487 Simpler customization of class creation
● no metaclasses, I promise you
● __init_subclass__ method will be called on base class when
a subclass is created
CPython improvements
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Python 3.6

● colection.OrderedDict is implemented in C and just faster
● os.scandir() provides faster way for directory traversal
● functools.lru_cache() has been reimplemented in C
● traceback is more handy for devs and faster too
Standard library improvements
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Python 3.5

● asyncio received new features and considered as stable
● typing has been improved and isn't in provisional state
● tracemalloc provides better output for memory allocation
errors
● pathlib has been improved and system path protocol is
implemented
Standard library improvements
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Python 3.6

Summary
● Use Python 3, asyncio and aiohttp for networking
applications
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Further reading
● @kakovskyi
○ Maintaining a high load Python project for newcomers
○ Maintaining a high load Python project: typical mistakes
○ Instant messenger with Python. Back-end development
○ How to easily find the optimal solution without exhaustive search
using Genetic Algorithms
● @bmwant
○ Asyncio-stack for web development
○ PEP8 is not enough
○ PyInvoke is your replacement for Makefile
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@kakovskyi
viach.kakovskyi@gmail.com
Questions?

Senior Platform Developers needed
tiny.cc/atlassian_atx
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