The document discusses a presentation on the benefits of type hints in Python. It provides an outline of the presentation which includes an introduction to type hints, how to use type hints, and the benefits of type hints. Some key benefits mentioned are improved code completion, the ability to catch type errors without running code, and using type hint tools for static type analysis.

1. Enjoy Type Hints
and its benefitsPython Conference Hong Kong 2018 Nov 22nd
in Cyberport, Hong Kong
Python Conference Hong Kong 2018 Nov 22nd 1

2. Python Conference Hong Kong 2018 Nov 22nd 2

3. Masato Nakamura(masahito)
• work at Nulab inc, Japn. Typetalk team
• use Scala and JavaScript and Python
• Python ❤ and
☕
❤
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4. Masato Nakamura(masahito)
• Speaker
• Plone Conference 2018 WebDays
• 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
You can use Type Hints from today!
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7. Not covering today
Technical Details
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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
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23. Traditional Python code(Python2)
Python 2.x series did not have a way to qualify function arguments
and return values, so many tools and libraries appeared to fill that
gap.
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24. Traditional Python code(Python2)
def greeting(name):
return 'Hello ' + name
greet = greeting("Masato")
• What is name
!
?
• What does greeting return
!
?
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25. PEP 3107(Python 3.0)
adding Function annotations, both for parameters and return
values, are completely optional.You can write free text .
def compile(source: "something compilable",
filename: "where the compilable thing comes from",
mode: "is this a single statement or a suite?"):
the semantics were deliberately left undefined.
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26. PEP 484(Python 3.5)
There has now been enough 3rd party usage for static type
analysis, that the community would benefit from a standardized
vocabulary and baseline tools within the standard library.
def greeting(name: str) -> str:
return 'Hello ' + name
• PEP-484 Type Hints
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27. Points in PEP484
Python will remain a dynamically typed language, and the authors
had no desire to ever make type hints mandatory, even by
convention.
• It’s not about code generation
• It’s not going to affect how your compiler complies your code.
• Your code can still break during run time after type checking.
• It’s not going to make Python static-typed
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28. inconvinient of PEP484
def greeting(name: str) -> str:
return 'Hello ' + name
greet = greeting("Masato") # type: str # make greeting message!
Hmm , now I'd like to describe variables more easily
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29. 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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30. typing module
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31. What is the typing module
• Module introduced when PEP 484 was implemented in 3.5
• Provides python with frequently used types such as List, Dict
• Make the data structure easier with namedtuple
from typing import List
a: List[int] = [1,2,3]
path: Optional[str] = None # Path to module sourde
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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'}
But let's use for Type Hints as much as possible for the future.
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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
# if you use Python 2.7 & 3.2-3.4
$ pip install typing
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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 3.6 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. Continuous Integration
• Jenkins
• Travis CI
• CircleCi
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55. 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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56. sample for CI
Sample
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57. example(error)
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58. example(success)
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59. Benefits for us
• We use Fabric 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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60. Recently, that date has been updated to January 1, 2020.
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61. We want to use Python3
• We use fabric3
• It's fabric for Python3
• https://pypi.python.org/pypi/Fabric3
• We try to check this, That's good for run
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62. We 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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63. Those are the Benefits of Type Hints
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64. Today's Outline
✅
1. Introduction of Type Hints
✅
2. Usage of Type Hints
✅
3. Benefits of Type Hints
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65. I hope you can try using Type
Hinting from today!
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66. Thank you
@masahito
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