Dalam versi baru Python, anotasi tipe mendapatkan lebih banyak dukungan, dan semakin banyak digunakan di perpustakaan, kerangka kerja, dan proyek Python. Selain dokumentasi tambahan dari kode tersebut, anotasi tipe memungkinkan alat seperti mypy untuk secara statis melakukan pemeriksaan validasi tambahan dan mengidentifikasi kemungkinan kesalahan dalam kode. Artikel ini akan berbicara tentang satu, saya pikir, topik yang menarik tentang pemeriksaan tipe statis dengan Python - protokol, atau seperti yang dinyatakan dalam PEP-544 , pengetikan bebek statis .
Kandungan
, Python, , - :
, , , ,
>>> class Meter:
... def __len__(self):
... return 1_000
...
>>> len([1, 2, 3])
3
>>> len("Duck typing...")
14
>>> len(Meter())
1000
len
, , __len__()
.
. , , – . .
(nominal type system) , , , . Duck
Bird
, Duck
, Bird
. Python, mypy , , , .
:
class Bird:
def feed(self) -> None:
print("Feeding the bird...")
class Duck(Bird):
def feed(self) -> None:
print("Feeding the duck...")
class Goose:
"""
- Bird.
"""
def feed(self) -> None:
print("Feeding the goose...")
def feed(bird: Bird) -> None:
bird.feed()
# OK
feed(Bird())
# OK
feed(Duck())
# Mypy error: Argument 1 to "feed" has incompatible type "Goose";
# expected "Bird"
feed(Goose())
# Mypy error: Argument 1 to "feed" has incompatible type "None";
# expected "Bird"
feed(None)
Goose
feed
, Bird
, mypy.
. , Java, C#, C++ .
(structural type system) , . , , compile time duck typing.
. , Go – , . , Go - , , .
– TypeScript, :
// TypeScript
interface Person {
name: String
age: Number
}
function show(person: Person) {
console.log("Name: " + person.name)
console.log("Age: " + person.age)
}
class Employee {
name: String
age: Number
constructor(name: String, age: Number) {
this.name = name
this.age = age
}
}
class Figure {}
// OK
show(new Employee("John", 30))
// OK
show({name: "Peter", age: 25})
// Error:
// Argument of type 'Figure' is not assignable to parameter of type 'Person'.
// Type 'Figure' is missing the following properties
// from type 'Person': name, age
show(new Figure())
Employee
Person
, . , Employee
name
age
. Figure
, , , , , Person
.
Python
Python 3.8 (PEP-544), Python. Python , . , , , , .
"" , ( , , mypy). , - , (abc.ABC
), .
:
import typing as t
# t.Iterable[int] -
def iterate_by(numbers: t.Iterable[int]) -> None:
for number in numbers:
print(number)
# OK
iterate_by([1, 2, 3])
# OK
iterate_by(range(1_000_000))
# Mypy error: Argument 1 to "iterate_by" has incompatible type "str";
# expected "Iterable[int]"
# note: Following member(s) of "str" have conflicts:
# note: Expected:
# note: def __iter__(self) -> Iterator[int]
# note: Got:
# note: def __iter__(self) -> Iterator[str]
iterate_by("duck")
Mypy , iterate_by
(, __iter__
).
, , mypy , .
# ...
class Fibonacci:
def __iter__(self) -> t.Iterator[int]:
a, b = 0, 1
while True:
yield a
a, b = b, a + b
# OK
iterate_by(Fibonacci())
class Animals:
"""
, ,
,
.
"""
def __iter__(self) -> t.Iterator[str]:
yield from ["duck", "cat", "dog"]
# Mypy error: Argument 1 to "iterate_by" has incompatible type "Animals";
# expected "Iterable[int]"
iterate_by(Animals())
( typing
) . mypy.
, . mypy , .
:
import typing as t
class Figure(t.Protocol):
""" ."""
# ,
name: str
def calculate_area(self) -> float:
""" ."""
def calculate_perimeter(self) -> float:
""" ."""
def show(figure: Figure) -> None:
print(f"S ({figure.name}) = {figure.calculate_area()}")
print(f"P ({figure.name}) = {figure.calculate_perimeter()}")
Protocol
typing
. - , . - ( -).
, Figure
.
# ...
class Square:
name = ""
def __init__(self, size: float):
self.size = size
def calculate_area(self) -> float:
return self.size * self.size
def calculate_perimeter(self) -> float:
return 4 * self.size
def set_color(self, color: str) -> None:
"""
,
.
"""
self.color = color
# OK
show(Square(size=3.14))
, Square
Figure
. Mypy show
Figure
, Square
. , . , Figure
show
, Square
– ( ). , .
, mypy :
# ...
class Circle:
PI = 3.1415926
name = ""
def __init__(self, radius: float):
self.radius = radius
def calculate_perimeter(self) -> float:
return 2 * self.PI * self.radius
# Mypy error: Argument 1 to "show" has incompatible type "Circle";
# expected "Figure"
# note: 'Circle' is missing following 'Figure' protocol member:
# note: calculate_area
show(Circle(radius=1))
mypy , ( ).
, , . mypy , .
import typing as t
import abc
class Readable(t.Protocol):
@abc.abstractmethod
def read(self) -> str:
...
def get_size(self) -> int:
"""
-.
"""
return 1_000
# OK
class File(Readable):
def read(self) -> str:
return " "
# OK
print(File().get_size()) # 1000
# Mypy error: Return type "int" of "read" incompatible
# with return type "str" in supertype "Readable"
class WrongFile(Readable):
def read(self) -> int:
return 42
(abc.ABC
), , -. , , mypy .
runtime_checkable
, isinstance
issubclass
. , , mypy :
# ... Figure
s = Square(4)
# Mypy error: Only @runtime_checkable protocols can be used
# with instance and class checks
# isinstance(s, Figure)
isinstance(s, Figure)
, @runtime_checkable
, .
import typing as t
@t.runtime_checkable
class HasLength(t.Protocol):
def __len__(self) -> int:
...
# OK
print(isinstance("", HasLength)) # True
print(isinstance([1, 2, 3], HasLength)) # True
- , , PEP-544.
Python, . Mypy Python. , , , , .
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Catatan (sunting)
Semua contoh yang dibahas dalam artikel ini diuji dengan Python 3.9 / mypy 0.812.
-
link yang berguna
-
PEP-544 - Protokol: Subtipe struktural
Mengetik Bebek (Istilah Python)
Sistem tipe nominal (Wikipedia)
Sistem tipe struktural (Wikipedia)
Protokol Iterator: Bagaimana "For Loops" Bekerja dengan Python
Protokol dan subtipe struktural (Dokumentasi mypy)
-