Slide is uploaded. You can see it via QR code or, via URL Chat(Element): #Conference 1: Optiver If you have a Combined or Conference Ticket, you can PEP8 styles in the sample code are ignored Due to space limitations. I'm sorry for hard to see Notes 3 / 49
Name: Peacock / Yoichi Takai Twitter / GitHub / Facebook: peacock0803sz Please call me Peacock I'm Attending from Japan, now it's 17:30 in JST Thanks for considering the timezone! Favourites: Music (Most is classical), Skiing, Gadgets Self-introduction 4 / 49
Company: CMScom (Full-time since 2020/06 ~) We're the only company in Japan that uses Plone Member of PloneJP (Plone User's Group in Japan) We created a short video to introducing Plone 6! https:/ /youtu.be/CtpccSyRJaY Operating Member of PyCon JP Association Staff of PyCon JP 2020, 2021 PyCon JP TV's director YouTube live about PyCons and local events held once a month 5 / 49
1. Why do I talk about typing? 2. Introduction of typing, How to write basically (I most want to say) 3. Generics, User-Defined types (Best practice included) 4. Updates overview recently & Backward compatibility for 3.9 or before 5. Overview of new features on 3.10 Today's topic 6 / 49
It's been five years since typing appeared In Python 3.5, at 2015 Several big PEPs were adopted and updated over the years Even now, I think many people don't know where to start Because there is little coherent information Why do I talk about typing? 7 / 49
Developing library with typing Configures and options of mypy How to use them in CI, ex: GitHub actions, Circle CI and etc... History of type hinting Implementation of typing, mypy Abstract Syntax Tree (AST) I will not talk about 8 / 49
It knows the type when you reference it in the editor. It gets angry when I try to give it the wrong one. The completion will work when accessing the return value of a function using a dot. What makes you happy? 10 / 49
After the arguments, write colon and type Before the colon at the end of the function definition, write an arrow and type Let's start with function definitions 15 / 49
Using built-in types bool , bytes , float , int , str you don't need to do anything to use them. None : used for functions that return nothing. Escaping from type puzzles Any Can hold instances of any type. It's better not to use it. Import and use from typing when necessary. from typing import Any
dict , frozenset , list , set , tuple Collections can be written with [] for the type inside. 3.9 and later only 3.7, 3.8 write from __future__ import annotaions (see below) 3.6: import annotations starting with uppercase letters from typing (next section) ref: official documentation (English) Since 3.9: Generics in standard Collections 17 / 49
Until 3.8, it was from typing , but now it's depreciated. For __builtins__ start with lowercase without doing anything. Such as list , tuple , and dict etc... For collections (ex: deque, defaultdict, ...), import modules start with collections iterable, callable, and other protocol-related items import modules start with collections.abc . regular expressions from re . Context-related items are available in contextlib . 18 / 49
For Generics, until 3.9, you had to write from typing import ... Such as Dict , List and Tuple etc... From 3.9, it's deprecated. from typing import Dict, List, Tuple, ... # before 3.9
There are many types in collections.abc . It's better to use a collection with a few methods to increase portability. The following figure shows the relationship. The further to the left you go, the fewer methods it has. To the right, the more methods it has. It's a good idea to look at the methods used in your functions. Choose the types on the left side of this diagram as much as possible. Using different types of collections 20 / 49
Tuples are fixed up to the length information Specify the type for the number of elements Or you can mix types, such as tuple[int, str, float]. A sequence, such as a list, has the same constraint for all elements in the element Can be used regardless of the length of the sequence by setting only one element. The difference between tuple and others Sequences 22 / 49
Shorthand, Optional[T] is equivalent to Union with None. Behaves just like Union: T | None If you use it in a function return value or something, it will propagate, so be careful how you use it. from typing import Optional
Optional is useful but causes code bloat. def get_content() -> str | None: r = request.get("https://example.com")
if r.status_code != 200: # This is the guard (early return)
logging.warning("HTTP response is %d!", r.status_code)
return None
return r.text
When you use the up function, you might write another guard and return None . As a result, we need to write a guard to the previous method, which reduces readability. Avoid using Optional as much as possible 26 / 49
In this case It would be cleaner to raise a raise RuntimeError . The cost of raising exceptions in Python is (relatively) low The performance would be satisfactory. The lack of null-safe methods in Python is also a factor But if there were such methods, they would be abused. Null-safe means a method that does not raise an exception when passed None. 27 / 49
It can be used when writing functions that take a function as an argument, such as decorator functions. from collections.abc import Callable # since 3.9 from typing import Callable # 3.8 and earlier
We are the biggest Python conference in Japan. Website: https:/ /2021.pycon.jp/ Blog: https:/ /pyconjp.blogspot.com/ Twitter: @pyconjapan Date(conference day): 10/15(Fri), 16(Sat) Sprint and Training is not determined Now, CfP is over In the process of review and adoption Announces about PyCon JP 2021 (1/2) 32 / 49
Venue: Online or Hybrid: On-site venue is Bellesalle Kanda, Tokyo 10/15(Fri) starts in the afternoon It'll be available only in the afternoon It may change depending on the COVID-19 situation 10/16(Sat): All online Sponsors application (second) is open: Blog post For the latest information, check our blog and Twitter Share this slide page with more Pythonistas around you! Announces about PyCon JP 2021 (2/2) 33 / 49
It exists for backward compatibility. Using typing new feature in the older versions, write from __future__ import annotations It describes when disruptive changes are introduced and become mandatory. In addition to typing, it was also used to call 3.x features in 2.x. ex) print_func , unicode_literals etc ... refs: __future__, future statement What is the __future__ module: (dunder future)? 36 / 49
The union above type can be used as an operator. You can also use it when asking isinstance() . More intuitive since TypeScipt and others use this notation. int | str == typing.Union[int, str] # Compatible with typing.Union
THIS TOPIC IS DIFFICULT!!! Motivation Tring to write a generic decorator, it's difficult to write the type Needed a way to represent a function that has the same arguments as the specified function PEP 612: Parameter Specification Variables 39 / 49
Approach Adding an argument type called ParameterSpecification solves the problem. It can be used with Callable to behave like a generic callable object. You can think of it as an argument version of TypeVar . 40 / 49
Motivation We consider global variables without type hints to be type aliases. This tends to cause problems with forwarding references, scoping, etc. So, we're going to make it possible to explicitly define type aliases. You can still define type aliases implicitly. PEP 613: TypeAlias 42 / 49
Approach Add a new typing.TypeAlias Write a variable of type alias type like T: TypeAlias = int Variables defined at the global level are considered type aliases. Using ForwardReference, you can write T: TypeAlias = "int" . Example x = 1 # untyped global expression
x: int = 1 # typed global expression
x = int # untyped global expression x: Type[int] = int # typed global expression
x: TypeAlias = int # type alias x: TypeAlias = “MyClass” # type alias
However, that will not work as intended if the user function is used. def is_str_list(val: List[object]) -> bool:
"""Determines whether all objects in the list are strings""" return all(isinstance(x, str) for x in val)
def func1(val: List[object]):
if is_str_list(val): print(" ".join(val)) # Error: invalid type TypeGuard allows you to define user-defined type guards via the new typing. By using user-defined type guards, it is easier to get support for type narrowing. 45 / 49
1. Introduction i. Motivation, Let's start writing, Built-in types ii. Standard collection type hints starting with lowercase (3.9) 2. Collections and Generics i. Union, Optional, Callable, User-defined Generics 3. Updates Overview & How to use new features in older versions 4. Python 3.10 style type hinting i. New Type Union Operator, Parameter Specific Variables, TypeAlias, User-Defined Type Guards Summary 47 / 49
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