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What's new in Python 3.7?
by Stéphane Wirtel
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I am Stéphane
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What's new in Python 3.7?
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A new Syntax!
public class Python37 {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
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PEP 537
PEP 553, Built-in breakpoint()
PEP 557, Data Classes
PEP 562, Module __getattr__ and __dir__
PEP 563, Postponed Evaluation of Annotations
PEP 564, Time functions with nanosecond resolution
PEP 565, Show DeprecationWarning in __main__
PEP 567, Context Variables
PEP 540, UTF-8 mode
https://www.python.org/dev/peps/pep-0537/
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PEP 553
Built-in breakpoint()
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
A wonderful function
def divide(e, f):
return f / e
a, b = 0, 1
print(divide(a, b))
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
A wonderful function
def divide(e, f):
return f / e
a, b = 0, 1
print(divide(a, b))
and of course, you have a crash...
Traceback (most recent call last):
File "bugs.py", line 5, in
print(divide(a, b))
File "bugs.py", line 2, in divide
return f / e
ZeroDivisionError: division by zero
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
So, how can I debug it? maybe with debugger (hello JS)?
def divide(e, f):
debugger;
return f / e
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
So, how can I debug it? maybe with debugger (hello JS)?
def divide(e, f):
debugger;
return f / e
No, it is not debugger, then what is the name of my debugger and how to add a breakpoint?
pdb
ipdb
pudb
pdbpp
...
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
for example, with pdb
def divide(e, f):
import pdb; pdb.set_trace()
return f / e
a, b = 0, 1
print(divide(a, b))
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
for example, with pdb
def divide(e, f):
import pdb; pdb.set_trace()
return f / e
a, b = 0, 1
print(divide(a, b))
or with pudb
def divide(e, f):
import pudb; pudb.set_trace()
return f / e
a, b = 0, 1
print(divide(a, b))
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
or just with breakpoint()
def divide(e, f):
breakpoint()
return f / e
a, b = 0, 1
print(divide(a, b))
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
or just with breakpoint()
def divide(e, f):
breakpoint()
return f / e
a, b = 0, 1
print(divide(a, b))
$ python bugs.py
> /tmp/bugs.py(3)divide()
-> return f / e
(Pdb)
By default, breakpoint will execute pdb.set_trace()
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
can be configured
$ PYTHONBREAKPOINT=0 python bugs.py
$ PYTHONBREAKPOINT='' python bugs.py
$ PYTHONBREAKPOINT=pudb.set_trace python bugs.py
$ PYTHONBREAKPOINT=IPython.embed python bugs.py
...
$ pip install web-pdb
$ PYTHONBREAKPOINT=’web_pdb.set_trace’ python bugs.py
https://www.python.org/dev/peps/pep-0553/
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Built-in breakpoint()
For example with web-pdb
https://www.python.org/dev/peps/pep-0553/
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PEP 557
Data Classes
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Introduction
Numerous attempts to define classes which exist primarily to store values
Examples
collections.namedtuple
The attrs project (Hi Hynek!)
with python classes
...
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Bad examples (tuple, dict)
tuple
>>> person = ('Foo', 'Bar')
>>> person[0] # is it the firstname or the lastname?
dict
>>> person = {'firstname': 'Foo', 'lastname': 'Bar'}
>>> person['firstname'] # would prefer the . notation
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Bad examples (namedtuple)
from collections import namedtuple
Person = namedtuple('Person', ['firstname', 'lastname'])
person = Person('Foo', 'Bar')
person.firstname
person == Person('Foo', 'Bar')
person == ('Foo', 'Bar')
# but
person.firstname = 'Foooooooooo' # will crash
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Bad examples (class)
class Person:
def __init__(self, firstname, lastname, age):
self.firstname = firstname
self.lastname = lastname
def __repr__(self):
return f'Person(firstname={self.firstname}, lastname={self.lastname})'
def __eq__(self, o):
return (self.firstname == o.firstname
and self.lastname == o.lastname)
def __lt__(self, o):
return (self.firstname < o.firstname
and self.lastname < o.lastname)
person = Person('Foo', 'Bar')
person.firstname
>>> person == Person('Foo', 'Bar')
True
>>> person < Person('Foo', 'Bar')
False
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Good example
from dataclasses import dataclass
@dataclass
class Person:
firstname: str
lastname: str
person = Person('Foo', 'Bar')
person.firstname
>>> person == Person('Foo', 'Bar')
True
https://www.python.org/dev/peps/pep-0557/
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Data Classes - make_dataclass
from dataclasses import make_dataclass
Person = make_dataclass('Person', ['firstname', 'lastname'])
person = Person('Foo', 'Bar')
https://www.python.org/dev/peps/pep-0557/
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Data Classes - default values
from dataclasses import dataclass
@dataclass
class Position:
name: str
latitude: float = 0.0
longitude: float = 0.0
>>> europython = Position('Charleroi')
Position(name='Charleroi', latitude=0.0, longitude=0.0)
https://www.python.org/dev/peps/pep-0557/
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Data Classes - default values
from typing import List
from dataclasses import dataclass, field
@dataclass
class Attendee:
firstname: str
lastname: str
def default_attendees() -> List[Attendees]:
return [Attendee('Foo', 'Bar')]
@dataclass
class Conference:
name: str
locations: str
attendees: List[Attendee] = field(default_factory=default_attendees)
conference = Conference('PySS18', 'San Sebastiàn')
assert isinstance(conference.attendees, list)
assert len(conference.attendees) == 1
https://www.python.org/dev/peps/pep-0557/
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Data Classes - methods/properties
from dataclasses import dataclass
@dataclass
class Person:
firstname: str
lastname: str
age: int
@property
def fullname(self):
return f'{self.firstname} {self.lastname}'
https://www.python.org/dev/peps/pep-0557/
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Data Classes - con guration
init=True => __init__
repr=True=> __repr__
eq=True => __eq__
order=False => __lt__, __le__, __gt__, __ge__
frozen=False => __setattr__, __getattr__ ...
https://www.python.org/dev/peps/pep-0557/
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Data Classes - con guration - frozen
from dataclasses import dataclass
@dataclass(frozen=True)
class Person:
firstname: str
lastname: str
age: int
>>> person = Person('Foo', 'Bar', 38)
>>> person.age = 27 # dataclasses.FrozenInstanceError: cannot assign to field 'age
https://www.python.org/dev/peps/pep-0557/
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Data Classes - con guration - order
from dataclasses import dataclass
@dataclass(order=True)
class Person:
firstname: str
lastname: str
age: int
>>> person = Person('Foo', 'Bar', 38)
>>> person < Person('Foo', 'Bar', 37)
False
https://www.python.org/dev/peps/pep-0557/
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Data Classes - inheritance
@dataclass
class Person:
firstname: str
lastname: str
@dataclass
class User(Person):
username: str
password: str
person = Person('Foo', 'Bar')
user = User('Foo', 'Bar', 'Us3rn4m3', 's3cr3t')
https://www.python.org/dev/peps/pep-0557/
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Data Classes - mypy
from dataclasses import dataclass
@dataclass
class Person:
firstname: str
lastname: str
person = Person(1, 2)
$ mypy demo_dataclass.py
...:8: error: Argument 1 to "Person" has incompatible type "int"; expected "str"
...:8: error: Argument 2 to "Person" has incompatible type "int"; expected "str"
https://www.python.org/dev/peps/pep-0557/
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Data Classes - asdict, astuple
You can also convert to a dict or a tuple
>>> from dataclasses import asdict, astuple
>>> person = Person('Foo', 'Bar')
>>> asdict(person)
{'firstname': 'Foo', 'lastname': 'Bar'}
>>> astuple(person)
('Foo', 'Bar')
https://www.python.org/dev/peps/pep-0557/
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Data Classes - Conclusion
replace tuples, namedtuples, simple class
use type annotation -> hello mypy
accept default values
can have logic via methods/properties
inheritance
helpers
https://www.python.org/dev/peps/pep-0557/
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PEP 562
Module __getattr__ and __dir__
https://www.python.org/dev/peps/pep-0562/
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Module __getattr__ and __dir__
Customize the access to an attribute of a module, example, a deprecated function
# main.py
from lib import old_function # Works, but emits the warning
$ python3 -Wd main.py
/tmp/demo/lib.py:11: DeprecationWarning: old_function is deprecated
https://www.python.org/dev/peps/pep-0562/
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Module __getattr__ and __dir__
# lib.py
from warnings import warn
def old_function(*args, **kwargs):
warn('old_function is deprecated', DeprecationWarning)
...
def old_other_function(*args, **kwargs):
warn('old_other_function is deprecated', DeprecationWarning)
...
https://www.python.org/dev/peps/pep-0562/
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Module __getattr__ and __dir__
# lib.py
from warnings import warn
deprecated_names = ['old_function', 'old_other_function']
def _deprecated_old_function(*args, **kwargs):
...
def _deprecated_old_other_function(*args, **kwargs):
...
def __getattr__(name):
if name in deprecated_names:
warn(f'{name} is deprecated', DeprecationWarning)
return globlals()[f'_deprectated_{name}']
raise AttributeError(f'module {__name__} has no attribute {name}')
https://www.python.org/dev/peps/pep-0562/
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Module __getattr__ and __dir__
Customize the listing of the items from a module
# lib.py
deprecated_names = ['old_function']
__all__ = ['new_function_one', 'new_function_two']
def new_function_one(arg, other):
...
def new_function_two(arg, other):
...
def __dir__() -> List[str]:
return sorted(__all__ + deprecated_names)
https://www.python.org/dev/peps/pep-0562/
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Module __getattr__ and __dir__
Customize the listing of the items from a module
# lib.py
deprecated_names = ['old_function']
__all__ = ['new_function_one', 'new_function_two']
def new_function_one(arg, other):
...
def new_function_two(arg, other):
...
def __dir__() -> List[str]:
return sorted(__all__ + deprecated_names)
# main.py
import lib
dir(lib) # prints ['new_function_one', 'new_function_two', 'old_function', ...]
https://www.python.org/dev/peps/pep-0562/
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PEP 563
Postponed Evaluation of Annotations
https://www.python.org/dev/peps/pep-0563/
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PEP 563: Postponed Evaluation of Annotations
Without the annotations
class Node:
def __init__(self, left: Node, right: Node) -> None:
self.left = left
self.right = right
https://www.python.org/dev/peps/pep-0563/
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PEP 563: Postponed Evaluation of Annotations
Without the annotations
class Node:
def __init__(self, left: Node, right: Node) -> None:
self.left = left
self.right = right
Traceback (most recent call last):
File "test_node.py", line 1, in
class Node:
File "test_node.py", line 2, in Node
def __init__(self, left: Node, right: Node) -> None:
NameError: name 'Node' is not defined
https://www.python.org/dev/peps/pep-0563/
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PEP 563: Postponed Evaluation of Annotations
Problem with the forward reference, for that, we have to define the class like that
class Node:
def __init__(self, left: 'Node', right: 'Node') -> None:
self.left = left
self.right = right
https://www.python.org/dev/peps/pep-0563/
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PEP 563: Postponed Evaluation of Annotations
Now, with the annotations
from __future__ import annotations
class Node:
def __init__(self, left: Node, right: Node) -> None:
self.left = left
self.right = right
and we do not need a forward reference.
https://www.python.org/dev/peps/pep-0563/
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PEP 563: Postponed Evaluation of Annotations
With the annotations and the dataclasses
from __future__ import annotations
from dataclasses import dataclass
from typing import Optional
@dataclass
class Node:
left: Optional[Node] = None
right: Optiona[Node] = None
root = Tree()
print(root)
https://www.python.org/dev/peps/pep-0563/
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PEP 564
Time functions with nanosecond resolution
https://www.python.org/dev/peps/pep-0564
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Time functions with nanosecond resolution
Float type limited to 104 days
The Python time.time() function returns the current time as a floating-point numberself.
Limited to 64 bits and in the IEEE 754 format. With this limitation, the float type starts to
lose nanoseconds after 104 days.
-> Precision loss
Example
On Python microbenchmarks, it's common to see function calls taking less than 100ns. A
difference of a few nanoseconds might become significant.
https://www.python.org/dev/peps/pep-0564
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Time functions with nanosecond resolution
time.clock_gettime_ns()
time.clock_settime_ns()
time.monotonic_ns()
time.perf_counter_ns()
time.process_time_ns()
time.time_ns()
https://www.python.org/dev/peps/pep-0564
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Time functions with nanosecond resolution
time.clock_gettime_ns()
time.clock_settime_ns()
time.monotonic_ns()
time.perf_counter_ns()
time.process_time_ns()
time.time_ns()
>>> time.monotonic()
154630.068913333
https://www.python.org/dev/peps/pep-0564
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Time functions with nanosecond resolution
time.clock_gettime_ns()
time.clock_settime_ns()
time.monotonic_ns()
time.perf_counter_ns()
time.process_time_ns()
time.time_ns()
>>> time.monotonic()
154630.068913333
>>> time.monotonic_ns()
154631543907219
https://www.python.org/dev/peps/pep-0564
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PEP 565
Show DeprecationWarning in main
https://www.python.org/dev/peps/pep-0565/
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Show DeprecationWarning in main
Since Python 3.2, the DeprecationWarning was hidden by default but:
Side Effect
only visible then running tests
https://www.python.org/dev/peps/pep-0565/
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Show DeprecationWarning in main
Since Python 3.2, the DeprecationWarning was hidden by default but:
Side Effect
only visible then running tests
with python 3.7
DeprecationWarning: displayed by default only in __main__ and when running tests.
https://www.python.org/dev/peps/pep-0565/
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Show DeprecationWarning in main
with python 3.6
$ $PWD/python --version
Python 3.6.7+
$ make PYTHON=$PWD/python -C Doc/ venv
$PWD/python -m venv ./venv
./venv/bin/python3 -m pip install -U Sphinx blurb
Collecting Sphinx
https://www.python.org/dev/peps/pep-0565/
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Show DeprecationWarning in main
with python 3.6
$ $PWD/python --version
Python 3.6.7+
$ make PYTHON=$PWD/python -C Doc/ venv
$PWD/python -m venv ./venv
./venv/bin/python3 -m pip install -U Sphinx blurb
Collecting Sphinx
with python 3.7
$ $PWD/python --version
Python 3.7.1+
$ make PYTHON=$PWD/python -C Doc/ venv
$PWD/python -m venv ./venv
./venv/bin/python3 -m pip install -U Sphinx blurb
pip/_vendor/urllib3/util/selectors.py:14: DeprecationWarning: Using or ...
pip/_vendor/urllib3/_collections.py:2: DeprecationWarning: Using or ...
...
Collecting Sphinx
https://www.python.org/dev/peps/pep-0565/
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PEP 567
Context Variables
https://www.python.org/dev/peps/pep-0567/
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PEP 567: Context Variables
For a synchronous environment, TLS is perfect but not for an asynchronous environment,
which in this case, the asynchronous tasks execute concurrently in the same OS thread.
This concept is similar to the TLS, but allows correctly keeping track of values per
asynchronous task.
one new module: contextvars
two objects: Context and ContextVar
https://www.python.org/dev/peps/pep-0567/
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PEP 567: Context Variables
import contextvars
current_user = contextsvars.ContextVar('current_user', default=None)
async def inner():
log.debug('Current User: %s', current_user.get())
@routes.get('/{name}')
async def handler(request):
current_user.set(request.match_info['name'])
await inner()
https://www.python.org/dev/peps/pep-0567/
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PEP 540
UTF-8 Mode
https://www.python.org/dev/peps/pep-0540/
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UTF-8 Mode
> python -X utf8 your_script.py
> PYTHONUTF8=1 python your_script.py
disabled by default
but automatically enabled if LC_ALL=POSIX or C
if enabled:
Python will use the utf-8 encoding, regardless the locale of the current platform.
sys.getfilesystemencoding() returns UTF-8
locale.getpreferredencoding() return UTF-8
sys.stdin & sys.stdout error handlers to surrogateescape (avoid a
UnicodeDecodeError)
https://www.python.org/dev/peps/pep-0540/
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PEP 545
Python documentation translations
https://www.python.org/dev/peps/pep-0545/
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Python documentation translations
Of course, we have the official documentation in English
But you can find it also in:
French
Japanese
Korean
Maybe in the future, YOU could add
German
Polish
Spanish
Ukrainian
...
We are waiting for your contributions ;-)
https://www.python.org/dev/peps/pep-0545/
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Not in PEPs
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importlib.resources
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importlib.resources
Load binary artifact from a package.
= to pkg_resources in features, but > in performance
we can read from File System, a zip file or anywhere.
https://docs.python.org/fr/3.7/library/importlib.html
https://www.youtube.com/watch?v=ZsGFU2qh73E
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importlib.resources
Load binary artifact from a package.
= to pkg_resources in features, but > in performance
we can read from File System, a zip file or anywhere.
My package
email/
├── __init__.py
└── tests
├── data
│ ├── __init__.py
│ └── message.eml
└── __init__.py
https://docs.python.org/fr/3.7/library/importlib.html
https://www.youtube.com/watch?v=ZsGFU2qh73E
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importlib.resources
read email/tests/data/message.eml
without importlib.resources
dirname = pathlib.Path(__file__).parent
data_path = dirname / 'tests' / 'data' / 'message.eml'
eml = data_path.read_bytes()
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importlib.resources
read email/tests/data/message.eml
without importlib.resources
dirname = pathlib.Path(__file__).parent
data_path = dirname / 'tests' / 'data' / 'message.eml'
eml = data_path.read_bytes()
with importlib.resources
eml = resources.read_binary('email.tests.data', 'message.eml')
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importlib.resources
read email/tests/data/message.eml
without importlib.resources
dirname = pathlib.Path(__file__).parent
data_path = dirname / 'tests' / 'data' / 'message.eml'
eml = data_path.read_bytes()
with importlib.resources
eml = resources.read_binary('email.tests.data', 'message.eml')
or with a context manager
with resources.path('email.tests.data', 'message.eml') as eml:
do_something(eml)
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importlib.resources
read email/tests/data/message.eml
without importlib.resources
dirname = pathlib.Path(__file__).parent
data_path = dirname / 'tests' / 'data' / 'message.eml'
eml = data_path.read_bytes()
with importlib.resources
eml = resources.read_binary('email.tests.data', 'message.eml')
or with a context manager
with resources.path('email.tests.data', 'message.eml') as eml:
do_something(eml)
or
import email.tests.data
with resources.parth(email.tests.data, 'message.eml') as eml:
do_something(eml)
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"Dict keeps insertion order"
is the ruling!
Introduced in Python 3.6.
Thanks to INADA Naoki
https://mail.python.org/pipermail/python-dev/2017-
December/151283.html
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"Dict keeps insertion order" is the ruling!
>>> d = {}
>>> d['name'] = 'pycon'
>>> d['location'] = 'san sebastian, spain'
>>> d['year'] = 2018
>>> d
{'name': 'pycon', 'location': 'san sebastian, spain', 'year': 2018}
>>>
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from ... import ...
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from ... import ...
$ python3 -c "from itertools import demo"
Traceback (most recent call last):
File "", line 1, in
ImportError: cannot import name 'demo'
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from ... import ...
$ python3 -c "from itertools import demo"
Traceback (most recent call last):
File "", line 1, in
ImportError: cannot import name 'demo'
$ /opt/cpython-3.7/bin/python3 -c "from itertools import demo"
Traceback (most recent call last):
File "", line 1, in
ImportError: cannot import name 'demo' from 'itertools' (unknown location)
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async & await
are
keywords!
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async & await are keywords!
For async
async = True
$ python /tmp/test_async.py
File "/tmp/test_async.py", line 1
async = True
^
SyntaxError: invalid syntax
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async & await are keywords!
For async
async = True
$ python /tmp/test_async.py
File "/tmp/test_async.py", line 1
async = True
^
SyntaxError: invalid syntax
and await
def await():
pass
$ python /tmp/test_await.py
File "test_await.py", line 1
def await():
^
SyntaxError: invalid syntax
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AsyncIO Improvements
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asyncio has a lot of improvements
Welcome to the asyncio.run function. Before, when you wanted to execute a coroutine for
asyncio, you needed to create a loop, etc...
async def amain():
async with aiohttp.ClientSession() as session:
async with session.get('https://www.python.org') as resp:
content = await resp.text()
print(content[:30])
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asyncio has a lot of improvements
Welcome to the asyncio.run function. Before, when you wanted to execute a coroutine for
asyncio, you needed to create a loop, etc...
async def amain():
async with aiohttp.ClientSession() as session:
async with session.get('https://www.python.org') as resp:
content = await resp.text()
print(content[:30])
# before
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(amain())
finally:
loop.close()
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asyncio has a lot of improvements
Welcome to the asyncio.run function. Before, when you wanted to execute a coroutine for
asyncio, you needed to create a loop, etc...
async def amain():
async with aiohttp.ClientSession() as session:
async with session.get('https://www.python.org') as resp:
content = await resp.text()
print(content[:30])
# before
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(amain())
finally:
loop.close()
# now
asyncio.run(amain())
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asyncio has a lot of improvements
New functions
asyncio supports contextvars
asyncio.create_task() -> asyncio.get_event_loop().create_task()
loop.start_tls()
asyncio.current_task()
asyncio.all_tasks()
loop.sock_sendfile(): use the os.sendfile (when possible + performance)
...
Performance improvements
asyncio.get_event_loop (+- 15 times faster).
asyncio.Future callback management has been optimized
asyncio.gather() - 15% faster
asyncio.sleep() - 2x faster
...
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Gifts for the developers
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Gifts for the developers
> python -X importtime -c 'import asyncio'
import time: self [us] | cumulative | imported package
import time: 381 | 381 | zipimport
import time: 2044 | 2044 | _frozen_importlib_external
import time: 197 | 197 | _codecs
import time: 1515 | 1712 | codecs
...
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Gifts for the developers
> python -X dev
enable the "development mode"
add additional runtime checks
install debug hooks for the memory allocators
enable the faulthandler module for a beautiful Python dump on a crash ;-)
enable the asyncio debug mode
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Performances
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and many improvements, bug xes...
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and ...
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Python 3.7 is a great vintage!
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