Python type hints allow annotating function and variable types in Python code. They were introduced in PEP 484 for Python 3.5 and provide documentation of types without runtime enforcement. Using type hints and tools like mypy enables type checking of code without execution, improving code quality and readability. They help with code completion, refactoring Python 2 code to Python 3, and catching type errors during development.

1. Python
PyCon Kyushu in Okinawa 2019 May 18th
in Ryukyu University, Okinawa
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2. Python - PyCon Kyushu in Okinawa 2019 May 18th 2

3. Who are you( )?
• (masahito)
• Typetalk Software Developer
• use Scala and JavaScript and Python
• Python ❤ and
☕
❤
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4. Masato Nakamura(masahito)
• Speaker
• Python Conference Hong Kong 2018
• Python Conference Kyushu 2018 in Japan
• Python Conference Taiwan 2017
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5. Nulab provide collaboration softwares.
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6. Today's Goal
Type Hints ?
Type Hints
Python2 to 3
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7. Not covering today
?
Technical Detail
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8. Today's Outline
Ⅰ. Introduction of Type Hints
Ⅱ. Usage of Type Hints
Ⅲ. Benefits of Type Hints
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9. Today's Outline
!
Ⅰ. Introduction of Type Hints
Ⅱ. Usage of Type Hints
Ⅲ. Benefits of Type Hints
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10. Introduction of Type Hints
• A. What is Type Hints function
• B. History of Type Hints
• C. typing module
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11. What is Type Hints function
We can write more Readable Codes.
We can annotate our codes only.
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12. What is Type Hints function
• Traditional Python code
def twice(num):
return num * 2
• using Type Hints
def twice(num: int) -> int:
return num * 2
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13. What is Type Hints function
also we can use Class!
class Car:
def __init__(self) -> None:
self.seats = 4
c: Car = Car()
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14. What is Type Hints function
• using Type Hints
def twice(num: int) -> int:
return num * 2
• C-language Code
int twice(int num) {
return num * 2;
}
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15. Difference of Type Hints and C code
• If you set wrong Type,We cannot show runtime error
def twice(num: int) -> int:
return num * 2.0
# expected `int` but use `str`
!
print(twice("hello"))
$ python set_wrong_type.py
$ hellohello ##
!
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16. hmm, What is TypeHints ???
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17. We can annotate our codes only.
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18. But You use library, e.g. mypy
$ mypy --python-version 3.7 example.py
example.py:5: error: Argument 1 to "twice" has incompatible type
"str"; expected "int"
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19. What is good point for checking type ???
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20. We can check our code without run codes.
• so we can re-write our Python2 code to Python3 more easily
• We can do it !!
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21. History of Type Hints
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22. History of Type Hints
implement PEP
Python 3.0 3107
Python 3.5 484
Ptyhon 3.6 526
Python 3.7 560, 561, 562,563
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23. Traditional Python code(Python2)
def greeting(name):
return 'Hello ' + name
greet = greeting("Guido")
• What is name
!
?
• What does greeting return
!
?
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24. PEP 3107(Python 3.0)
def compile(source: "something compilable",
filename: "where the compilable thing comes from",
mode: "is this a single statement or a suite?"):
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25. PEP 484(Python 3.5)
def greeting(name: str) -> str:
return 'Hello ' + name
• PEP-484 Type Hints
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26. Points in PEP484
Python dynamically typed language
•
•
•
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27. inconvinient of PEP484
def greeting(name: str) -> str:
return 'Hello ' + name
greet = greeting("Masato") # type: str # make greeting message!
Hmm ,
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28. PEP 526(Python 3.6)
# PEP 484
def greeting(name: str) -> str:
return 'Hello ' + name
greet = greeting("Masato") # type: str # make greeting message!
# pep 526
def greeting(name: str) -> str:
return 'Hello ' + name
greet:str = greeting("Masato") # make greeting message!
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29. typing module
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30. What is the typing module
• PEP 484 3.5
• List,Dict,Union Python
• namedtuple
from typing import List
a: List[int] = [1,2,3]
path: Optional[str] = None # Path to module sourde
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31. • Union
i = 1 # Infer type "int" for i
l = [1, 2] # Infer type "List[int]" for l
from typing import Union
x: Union[int, str] = 1
x: Union[int, str] = 1.1 # Error
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32. • NamedTuple
In Python 3.5(PEP 484)
Point = namedtuple('Point', ['x', 'y'])
p = Point(x=1, y=2)
In Python 3.6(PEP 526)
from typing import NamedTuple
class Point(NamedTuple):
x: int
y: int
p = Point(x=1, y=2)
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33. Today's Outline
Ⅰ. Introduction of Type Hints
!
Ⅱ. Usage of Type Hints
Ⅲ. Benefits of Type Hints
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34. Usage Of Type Hints
• A. How to write
• B. How to get Type Hints Info
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35. How to write
PEP526 style
def greeting(name: str) -> str:
return 'Hello ' + name
greet: str = greeting("Masato")
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36. difference of PEP484 and PEP526
# pep 484
child # type: bool # cannot allow
if age < 18:
child = True # type: bool # It's OK
else:
child = False # type: bool # It's OK
# pep 526
child: bool # OK
if age < 18:
child = True # No need to Write bool
else:
child = False
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37. backward compatibility
# We can write pep484 style code in 3.6 backward compatiblity
hour = 24 # type: int
# PEP 526 style
hour: int; hour = 24
hour: int = 24
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38. recommend using Type Hints
PEP3107 style is also OK
>>> alice: 'well done' = 'A+'
>>> bob: 'what a shame' = 'F-'
>>> __annotations__
{'alice': 'well done', 'bob': 'what a shame'}
Type Hints
.
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39. How to get Type Hints Info
Q. where is variable annotation
A. at __annotaitons__
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40. How to get Type Hints Info
example
>>> answer:int = 42
>>> __annotations__
{'answer': <class 'int'>}
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41. Note for Class
We can only find Class variables.
>>> class Car:
... stats: ClassVar[Dict[str, int]] = {}
... def __init__(self) -> None:
... self.seats = 4
>>> c: Car = Car()
>>> c.__annotations__
{'stats': typing.ClassVar[typing.Dict[str, int]]}
# only ClassVar!
We cannot get instance's variables!
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42. Today's Outline
Ⅰ. Introduction of Type Hints
Ⅱ. Usage of Type Hints
!
Ⅲ. Benefits of Type Hints
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43. Benefits of Type Hints
A. Code Style
B. code completion
C. statistic type analysis
D. Our story
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44. Code Style
• Simple is best
• Explicit is better than Implicit.
def greeting(name: str) -> str:
return 'Hello ' + name
We can check this by Type Hints
def greeting(name: str) -> str:
return 42
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45. Code Completion
We can use code completion in
• Editor
• Visual Studio code
• IDE
• PyCharm(IntelliJ)
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46. example
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47. statistic type analysis
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48. statistic type analysis
• for check variable type(no runable code)
• python has some tools
• mypy
• pytypes (not talk)
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49. example
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50. mypy
• https://github.com/python/mypy
• made by JukkaL & Guido
• can output report
• We can use!(PEP526 style)
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51. How to install mypy
$ pip install mypy
Notice requires Python 3.5 or later to run.
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52. mypy example
• code(example.py)
from typing import NamedTuple
class Employee(NamedTuple):
name: str
id: int
emp: Employee = Employee(name='Guido', id='x')
• run
$ mypy --python-version 3.7 example.py
example.py:16: error: Argument 2 to "Employee" has incompatible type
"str"; expected "int"
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53. mypy can use in Python2
class MyClass(object):
# For instance methods, omit `self`.
def my_method(self, num, str1):
# type: (int, str) -> str
return num * str1
def __init__(self):
# type: () -> None
pass
x = MyClass() # type: MyClass
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54. Missing imports
import type annotation
!
main.py:1: error: No library stub file for standard library module 'antigravity'
main.py:2: error: No library stub file for module 'flask'
main.py:3: error: Cannot find module named 'this_module_does_not_exist'
( )
mypy --ignore-missing-imports
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55. Continuous Integration
• Jenkins
• Travis CI
• CircleCi
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56. Continuous Integration
• we can run mypy on CI systems
• we can get results
• If you develop in a team, there are many benefits
• ex: If someone issues a pull request for your project, you can
review their code
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57. sample for CI
Sample
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58. example(error)
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59. example(success)
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60. Benefits for us(Nulab)
• We use Fabric v1 and Ansible for deployment
• But it is for Only Python2
• Python2 will finished at 2020(Tokyo Olympic Year)
• We thought we should convert Python2 to Python3
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61. Recently, that date has been updated to January 1, 2020.
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62. We want to use Python3
• We use Fabric3
• It's Fabric for Python2.7 and Python3
• https://pypi.python.org/pypi/Fabric3
• We try to check this, That's good for run
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63. We(Nulab) use Python3 & Fabric3 & mypy
• We use TypeHints for rewriting our code
• We got it! -> Only 2days
• We deploy the new version of Out App every week.
• beta version every day!
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64. Python2 to 3
• Python2.7
• six ( Python2 3 )
• 2to3
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65. Python2 to 3
•
•
•
• ->
•
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66. def is_modified(path, backup='bak'):
# type: (Text, str) -> bool
"""
path
"""
with settings(hide('warnings'), warn_only=True):
result = sudo('diff -u %s.%s %s' % (path, backup, path))
return result.return_code == 1
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67. Those are the Benefits of Type Hints
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68. Today's Outline
✅
1. Introduction of Type Hints
✅
2. Usage of Type Hints
✅
3. Benefits of Type Hints
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69. ?
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70. Thank you
@masahito
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71. • type-hints pep
• PEP 586 -- Literal Types
• PEP 591 -- Adding a final qualifier to typing
• mypy (plugin)
• typing module
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72. PEP 586 -- Literal Types
from typing import Literal
def accepts_only_four(x: Literal[4]) -> None:
pass
accepts_only_four(4) # OK
accepts_only_four(19) # Rejected
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73. PEP 591 -- Adding a final qualifier to typing
from typing import Final
RATE: Final = 3000
class Base:
DEFAULT_ID: Final = 0
RATE = 300 # Error: can't assign to final attribute
Base.DEFAULT_ID = 1 # Error: can't override a final attribute
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74. mypy plugin
• mypy
• plugin mypy plugin
• sqlAlchemy etc
plugin
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75. mypy plugin
• dropbox SqlAlchemy mypy-stub
• https://github.com/python/mypy/issues/3538
• https://github.com/dropbox/sqlalchemy-stubs
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76. mypy PEP561
• PEP 561 is
•
• numpy stub
• https://github.com/numpy/numpy-stubs
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77. typing extentions
• typing
https://github.com/python/typing/tree/master/
typing_extensions
• Protocol
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78. User Defined Protocol
from typing import Iterable
from typing_extensions import Protocol
class SupportsClose(Protocol):
def close(self) -> None:
... # Empty method body (explicit '...')
class Resource: # No SupportsClose base class!
# ... some methods ...
def close(self) -> None:
self.resource.release()
def close_all(items: Iterable[SupportsClose]) -> None:
for item in items:
item.close()
close_all([Resource(), open('some/file')]) # Okay!
DuckTyping
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79. Thanks again!
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