使用 mypy 做 type check

前言

完残！😂，最近看之前写的 Python 代码老得琢磨这比变量的类型是啥（~~Python 无类型系统xxx~~），不愧是我写的！

看段之前写的实现迭代器模式的代码：

# 抽象迭代器类
class Iterator(object):def hasNext():passdef next():pass# 抽象聚集类
class Aggregate(object):def iterator():passclass BookShelf(Aggregate):def __init__(self):self._books = []self._last = 0def getBookAt(self, index):return self._books[index]def appendBook(self, book):self._books.append(book)self._last = self._last + 1def getLength(self):return self._lastdef iterator(self):return BookShelfIterator(self)class BookShelfIterator(Iterator):def __init__(self, bookShelf):self._bookShelf = bookShelfself._index = 0def hasNext(self):if self._index < self._bookShelf.getLength():return Trueelse:return Falsedef next(self):book = self._bookShelf.getBookAt(self._index)self._index = self._index + 1return bookclass Book():def __init__(self, name):self._name = namedef getName(self):return self._nameif __name__ == "__main__":bookShelf = BookShelf()bookShelf.appendBook(Book("A"))bookShelf.appendBook(Book("B"))bookShelf.appendBook(Book("C"))bookShelf.appendBook(Book("D"))it = bookShelf.iterator()while it.hasNext():book = it.next()print(book.getName())

有一丢丢难读（不通读的话，会乱猜某变量类型），回想之前在 PyCon China 2019 的大会资聊曾看到过类型检查相关的演讲主题，回顾下演讲视频。水一波，写篇文章了解下 Python 标准(PEP 3107 & PEP 484 )支持的 mypy。

类型系统：编译期的类型推导检查规则，类型系统属于一种轻量级的形式化方法（一种数学方法）

使用-mypy

# 安装 mypy
pip install mypy
# 使用 mypy 做类型检查
mypy module_name.py

以下使用方式适用于 Python 3.6 及以上的版本。值得注意：mypy 默认的推导类型不可为 None

变量的类型注释

integer: int = 1
string: str = "ShanSan"
err_str: str = 1  # error: Incompatible types in assignment
child: bool = True
# mypy 默认的推导类型不可为 None
none: int - None  # error: Invalid type comment or annotationprint(integer, string)

内建类型

关于更多 mypy 的类型系统内建的类型可参考：https://mypy.readthedocs.io/en/stable/builtin_types.html

from typing import Dict, Tuple, Optional, Iterable, Union
# 对于映射(Map)数据结构，需要指定 key 和 value 的类型
x: Dict[str, float] = {'field': 2.0}# Tuple 需要指定所有元素的类型
x: Tuple[int, str, float] = (3, "yes", 7.5)# error: Incompatible types in assignment (expression has type "Tuple[int, str, float, int]", variable has type "Tuple[int, str, float]")
y: Tuple[int, str, float] = (3, "yes", 7.5, 11)op: Optional[str] = None  # 可为 str 或 None# 泛用可迭代对象
l: Iterable = [1]
t: Iterable = (1, 2)
d: Iterable = {1: 1}# 可为 str 或 int
str_int1: Union[str, int] = 1
str_int2: Union[str, int] = "ss"
str_int3: Union[str, int] = None  # error

函数注解

from typing import NoReturndef f1() -> None:passdef f2() -> NoReturn:  # 无返回值passdef plus(num1: int, num2: int) -> int:return num1 + num2# 带默认值
def plus_default(num1: int, num2: int = 3) -> int:return num1 + num2# 容器的参数类型
def container_param(names: List[str]) -> None:for name in names:print(name)

类成员注解

class MyClass:attr: int# 带默认值的实例变量charge_percent: int = 100# 没有任何返回值应该注解为 Nonedef __init__(self) -> None:pass# 忽略对 self 类型的注解def my_method(self, num: int, str1: str) -> str:return num * str1# 支持自定义类型的注解
x: MyClass = MyClass()

结尾

OK，差不多了，对之前的迭代器模式的代码改造一波

from typing import List, Iterable# 抽象迭代器类
class Iterator(object):def hasNext(self):passdef next(self):pass# 抽象聚集类
class Aggregate(object):def iterator(self):passclass BookShelf(Aggregate):def __init__(self) -> None:self._books: List[Book] = []self._last: int = 0def getBookAt(self, index: int) -> Book:return self._books[index]def appendBook(self, book: Book) -> None:self._books.append(book)self._last = self._last + 1def getLength(self) -> int:return self._lastdef iterator(self) -> BookShelfIterator:return BookShelfIterator(self)class BookShelfIterator(Iterator):def __init__(self, bookShelf) -> None:self._bookShelf: BookShelf = bookShelfself._index: int = 0def hasNext(self) -> bool:if self._index < self._bookShelf.getLength():return Trueelse:return Falsedef next(self) -> Book:book: Book = self._bookShelf.getBookAt(self._index)self._index = self._index + 1return bookclass Book():def __init__(self, name) -> None:self._name: str = namedef getName(self) -> str:return self._nameif __name__ == "__main__":bookShelf: BookShelf = BookShelf()bookShelf.appendBook(Book("A"))bookShelf.appendBook(Book("B"))bookShelf.appendBook(Book("C"))bookShelf.appendBook(Book("D"))it: Iterator = bookShelf.iterator()while it.hasNext():book: Book = it.next()print(book.getName())

emmm, 舒服了一丢丢/(ㄒoㄒ)/~~