Python标准库之typing的用法(类型标注)

def f(a: str, b:int) -> str:
    return a * b

import typing
Id = typing.NewType("Id", int)
a = Id(2020)

from typing import Callable
def f(a: int) -> str:
    return str(a)
def callback(a: int, func: Callable[[int], str]) -> str:
    return func(a)
print(callback(1, f))

from typing import Mapping
a: Mapping[str, str]

from typing import TypeVar
T = TypeVar('T') # 可以是任何东西。
A = TypeVar('A', str, bytes) # 必须是 str 或 bytes

T = TypeVar('T', str)

AbstractSet = typing.AbstractSet
Any = typing.Any
AnyStr = ~AnyStr
AsyncContextManager = typing.AbstractAsyncContextManager
AsyncGenerator = typing.AsyncGenerator
AsyncIterable = typing.AsyncIterable
AsyncIterator = typing.AsyncIterator
Awaitable = typing.Awaitable
ByteString = typing.ByteString
Callable = typing.Callable
ClassVar = typing.ClassVar
Collection = typing.Collection
Container = typing.Container
ContextManager = typing.AbstractContextManager
Coroutine = typing.Coroutine
Counter = typing.Counter
DefaultDict = typing.DefaultDict
Deque = typing.Deque
Dict = typing.Dict
FrozenSet = typing.FrozenSet
Generator = typing.Generator
Hashable = typing.Hashable
ItemsView = typing.ItemsView
Iterable = typing.Iterable
Iterator = typing.Iterator
KeysView = typing.KeysView
List = typing.List
Mapping = typing.Mapping
MappingView = typing.MappingView
MutableMapping = typing.MutableMapping
MutableSequence = typing.MutableSequence
MutableSet = typing.MutableSet
NoReturn = typing.NoReturn
Optional = typing.Optional
Reversible = typing.Reversible
Sequence = typing.Sequence
Set = typing.Set
Sized = typing.Sized
TYPE_CHECKING = False
Tuple = typing.Tuple
Type = typing.Type
Union = typing.Union
ValuesView = typing.ValuesView

#一个典型的函数注释例子，为参数加上了类型
def greeting(name: str) -> str:
    return 'Hello ' + name

# 使用注释来标明变量类型
primes = [] # type:list[int]
captain = ... #type:str
class Starship:
    stats = {} #type:Dict[str,int]
primes:List[int] = []
captain:str #Note: no initial value
class Starship:
    stats: ClassVar[Dict[str,int]] = {}

from typing import List
Vector = List[float]
def scale(scalar: float, vector: Vector)->Vector:
    return [scalar*num for num in vector]
new_vector = scale(2.0, [1.0, -4.2, 5.4])

from typing import Dict, Tuple, List
ConnectionOptions = Dict[str, str]
Address = Tuple[str, int]
Server = Tuple[Address, ConnectionOptions]
def broadcast_message(message: str, servers: List[Server]) -> None:
    ...
# The static type checker will treat the previous type signature as
# being exactly equivalent to this one.
def broadcast_message(
        message: str,
        servers: List[Tuple[Tuple[str, int], Dict[str, str]]]) -> None:
    pass

form typing import NewType
UserId = NewType("UserId", int)
some_id = UserId(524313)

def get_user_name(user_id: UserId) -> str:
    pass
# typechecks
user_a = get_user_name(UserId(42351))
# does not typecheck; an int is not a UserId
user_b = get_user_name(-1)

# output仍然是int类型而不是UserId类型
output = UserId(23413) + UserId(54341)

from typing import NewType
UserId = NewType('UserId', int)
# Fails at runtime and does not typecheck
class AdminUserId(UserId): pass

from typing import NewType
UserId = NewType('UserId', int)
ProUserId = NewType('ProUserId', UserId)

from typing import Callable
def feeder(get_next_item: Callable[[], str]) -> None:
    # Body
def async_query(on_success: Callable[[int], None],
                on_error: Callable[[int, Exception], None]) -> None:
    # Body

from typing import Mapping, Sequence
def notify_by_email(employees: Sequence[Employee],
                    overrides: Mapping[str, str]) -> None: ...
 

from typing import Sequence, TypeVar
T = TypeVar('T')      # 申明类型变量
def first(l: Sequence[T]) -> T:   # Generic function
    return l[0]

from typing import TypeVar, Generic
from logging import Logger
T = TypeVar('T')
class LoggedVar(Generic[T]):
    def __init__(self, value: T, name: str, logger: Logger) -> None:
        self.name = name
        self.logger = logger
        self.value = value
    def set(self, new: T) -> None:
        self.log('Set ' + repr(self.value))
        self.value = new
    def get(self) -> T:
        self.log('Get ' + repr(self.value))
        return self.value
    def log(self, message: str) -> None:
        self.logger.info('%s: %s', self.name, message)

from typing import Iterable
def zero_all_vars(vars: Iterable[LoggedVar[int]]) -> None:
    for var in vars:
        var.set(0)

from typing import TypeVar, Generic
...
T = TypeVar('T')
S = TypeVar('S', int, str)
class StrangePair(Generic[T, S]):
    ...

from typing import TypeVar, Generic
...
T = TypeVar('T')
class Pair(Generic[T, T]):   # INVALID
    ...

from typing import TypeVar, Generic, Sized
T = TypeVar('T')
class LinkedList(Sized, Generic[T]):
    ... 

from typing import TypeVar, Mapping
T = TypeVar('T')
class MyDict(Mapping[str, T]):
    ...

from typing import Iterable
class MyIterable(Iterable): # Same as Iterable[Any]

from typing import TypeVar, Iterable, Tuple, Union
S = TypeVar('S')
Response = Union[Iterable[S], int]
# Return type here is same as Union[Iterable[str], int]
def response(query: str) -> Response[str]:
    ...
T = TypeVar('T', int, float, complex)
Vec = Iterable[Tuple[T, T]]
def inproduct(v: Vec[T]) -> T: # Same as Iterable[Tuple[T, T]]
    return sum(x*y for x, y in v)

from typing import Any
a = None    # type: Any
a = []      # OK
a = 2       # OK
s = ''      # type: str
s = a       # OK
def foo(item: Any) -> int:
    # Typechecks; 'item' could be any type,
    # and that type might have a 'bar' method
    item.bar()
    ...