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Pythonhttps://blog.csdn.net/weixin_45791458/category_12403403.html?spm=1001.2014.3001.5482

在python中，一切数据类型都是对象（即类的实例），包括整数、浮点数、字符串、列表、元组、集合、字典、复数、布尔、函数、自定义类等，它们都是根据相应的类创建的。

python内建类的定义可以在库文件/stdlib/builtins.pyi中找到，下面的例1示例性地给出了整数类型的定义。

# 例1 class int: @overload def __new__(cls, x: ConvertibleToInt = ..., /) -> Self: ... @overload def __new__(cls, x: str | bytes | bytearray, /, base: SupportsIndex) -> Self: ... def as_integer_ratio(self) -> tuple[int, Literal[1]]: ... @property def real(self) -> int: ... @property def imag(self) -> Literal[0]: ... @property def numerator(self) -> int: ... @property def denominator(self) -> Literal[1]: ... def conjugate(self) -> int: ... def bit_length(self) -> int: ... if sys.version_info >= (3, 10): def bit_count(self) -> int: ... if sys.version_info >= (3, 11): def to_bytes( self, length: SupportsIndex = 1, byteorder: Literal["little", "big"] = "big", *, signed: bool = False ) -> bytes: ... @classmethod def from_bytes( cls, bytes: Iterable[SupportsIndex] | SupportsBytes | ReadableBuffer, byteorder: Literal["little", "big"] = "big", *, signed: bool = False, ) -> Self: ... else: def to_bytes(self, length: SupportsIndex, byteorder: Literal["little", "big"], *, signed: bool = False) -> bytes: ... @classmethod def from_bytes( cls, bytes: Iterable[SupportsIndex] | SupportsBytes | ReadableBuffer, byteorder: Literal["little", "big"], *, signed: bool = False, ) -> Self: ... if sys.version_info >= (3, 12): def is_integer(self) -> Literal[True]: ... def __add__(self, value: int, /) -> int: ... def __sub__(self, value: int, /) -> int: ... def __mul__(self, value: int, /) -> int: ... def __floordiv__(self, value: int, /) -> int: ... def __truediv__(self, value: int, /) -> float: ... def __mod__(self, value: int, /) -> int: ... def __divmod__(self, value: int, /) -> tuple[int, int]: ... def __radd__(self, value: int, /) -> int: ... def __rsub__(self, value: int, /) -> int: ... def __rmul__(self, value: int, /) -> int: ... def __rfloordiv__(self, value: int, /) -> int: ... def __rtruediv__(self, value: int, /) -> float: ... def __rmod__(self, value: int, /) -> int: ... def __rdivmod__(self, value: int, /) -> tuple[int, int]: ... @overload def __pow__(self, x: Literal[0], /) -> Literal[1]: ... @overload def __pow__(self, value: Literal[0], mod: None, /) -> Literal[1]: ... @overload def __pow__(self, value: _PositiveInteger, mod: None = None, /) -> int: ... @overload def __pow__(self, value: _NegativeInteger, mod: None = None, /) -> float: ... # positive __value -> int; negative __value -> float # return type must be Any as `int | float` causes too many false-positive errors @overload def __pow__(self, value: int, mod: None = None, /) -> Any: ... @overload def __pow__(self, value: int, mod: int, /) -> int: ... def __rpow__(self, value: int, mod: int | None = None, /) -> Any: ... def __and__(self, value: int, /) -> int: ... def __or__(self, value: int, /) -> int: ... def __xor__(self, value: int, /) -> int: ... def __lshift__(self, value: int, /) -> int: ... def __rshift__(self, value: int, /) -> int: ... def __rand__(self, value: int, /) -> int: ... def __ror__(self, value: int, /) -> int: ... def __rxor__(self, value: int, /) -> int: ... def __rlshift__(self, value: int, /) -> int: ... def __rrshift__(self, value: int, /) -> int: ... def __neg__(self) -> int: ... def __pos__(self) -> int: ... def __invert__(self) -> int: ... def __trunc__(self) -> int: ... def __ceil__(self) -> int: ... def __floor__(self) -> int: ... def __round__(self, ndigits: SupportsIndex = ..., /) -> int: ... def __getnewargs__(self) -> tuple[int]: ... def __eq__(self, value: object, /) -> bool: ... def __ne__(self, value: object, /) -> bool: ... def __lt__(self, value: int, /) -> bool: ... def __le__(self, value: int, /) -> bool: ... def __gt__(self, value: int, /) -> bool: ... def __ge__(self, value: int, /) -> bool: ... def __float__(self) -> float: ... def __int__(self) -> int: ... def __abs__(self) -> int: ... def __hash__(self) -> int: ... def __bool__(self) -> bool: ... def __index__(self) -> int: ...

如果一个类没有指定父类，则其默认继承object类，它是python中所有类的基类，如例2所示，注意在最后使用了issubclass函数进行了检验。

# 例2 class object: __doc__: str | None __dict__: dict[str, Any] __module__: str __annotations__: dict[str, Any] @property def __class__(self) -> type[Self]: ... # 注意这个属性 @__class__.setter def __class__(self, type: type[object], /) -> None: ... def __init__(self) -> None: ... def __new__(cls) -> Self: ... # N.B. `object.__setattr__` and `object.__delattr__` are heavily special-cased by type checkers. # Overriding them in subclasses has different semantics, even if the override has an identical signature. def __setattr__(self, name: str, value: Any, /) -> None: ... def __delattr__(self, name: str, /) -> None: ... def __eq__(self, value: object, /) -> bool: ... def __ne__(self, value: object, /) -> bool: ... def __str__(self) -> str: ... # noqa: Y029 def __repr__(self) -> str: ... # noqa: Y029 def __hash__(self) -> int: ... def __format__(self, format_spec: str, /) -> str: ... def __getattribute__(self, name: str, /) -> Any: ... def __sizeof__(self) -> int: ... # return type of pickle methods is rather hard to express in the current type system # see #6661 and https://docs.python.org/3/library/pickle.html#object.__reduce__ def __reduce__(self) -> str | tuple[Any, ...]: ... def __reduce_ex__(self, protocol: SupportsIndex, /) -> str | tuple[Any, ...]: ... if sys.version_info >= (3, 11): def __getstate__(self) -> object: ... def __dir__(self) -> Iterable[str]: ... def __init_subclass__(cls) -> None: ... @classmethod def __subclasshook__(cls, subclass: type, /) -> bool: ... print(issubclass(int, object)) # 注意使用类名int而不是int() # 输出 True

type是一个python内置类，例3是它的定义，如所有其他类一样，它也继承了object类。

# 例3 class type: # object.__base__ is None. Otherwise, it would be a type. @property def __base__(self) -> type | None: ... __bases__: tuple[type, ...] @property def __basicsize__(self) -> int: ... @property def __dict__(self) -> types.MappingProxyType[str, Any]: ... # type: ignore[override] @property def __dictoffset__(self) -> int: ... @property def __flags__(self) -> int: ... @property def __itemsize__(self) -> int: ... __module__: str @property def __mro__(self) -> tuple[type, ...]: ... __name__: str __qualname__: str @property def __text_signature__(self) -> str | None: ... @property def __weakrefoffset__(self) -> int: ... @overload def __init__(self, o: object, /) -> None: ... @overload def __init__(self, name: str, bases: tuple[type, ...], dict: dict[str, Any], /, **kwds: Any) -> None: ... @overload def __new__(cls, o: object, /) -> type: ... @overload def __new__( cls: type[_typeshed.Self], name: str, bases: tuple[type, ...], namespace: dict[str, Any], /, **kwds: Any ) -> _typeshed.Self: ... def __call__(self, *args: Any, **kwds: Any) -> Any: ... def __subclasses__(self: _typeshed.Self) -> list[_typeshed.Self]: ... # Note: the documentation doesn't specify what the return type is, the standard # implementation seems to be returning a list. def mro(self) -> list[type]: ... def __instancecheck__(self, instance: Any, /) -> bool: ... def __subclasscheck__(self, subclass: type, /) -> bool: ... @classmethod def __prepare__(metacls, name: str, bases: tuple[type, ...], /, **kwds: Any) -> MutableMapping[str, object]: ... if sys.version_info >= (3, 10): def __or__(self, value: Any, /) -> types.UnionType: ... def __ror__(self, value: Any, /) -> types.UnionType: ... if sys.version_info >= (3, 12): __type_params__: tuple[TypeVar | ParamSpec | TypeVarTuple, ...] print(issubclass(type, object)) # 注意使用类名type而不是type() # 输出 True

type()类可以返回一个对象（即类的实例）的类，它实际上是返回一个对象（即类的实例）的__class__属性，而__class__属性在例化一个类时会自动设置，下面的例4说明了这一点。

# 例4 a=1 b=1.0 c="1" d=[1,2,3] e=(1,2,3) f={1,2,3} g={"a":1,"b":2} h=1+2j i=True def j(): pass class k: pass kk=k() print(type(a), a.__class__, issubclass(type(a), object)) print(type(b), b.__class__, issubclass(type(b), object)) print(type(c), c.__class__, issubclass(type(c), object)) print(type(d), d.__class__, issubclass(type(d), object)) print(type(e), e.__class__, issubclass(type(e), object)) print(type(f), f.__class__, issubclass(type(f), object)) print(type(g), g.__class__, issubclass(type(g), object)) print(type(h), h.__class__, issubclass(type(h), object)) print(type(i), i.__class__, issubclass(type(i), object)) print(type(j), j.__class__, issubclass(type(j), object)) print(type(kk), kk.__class__, issubclass(type(kk), object)) # 输出 <class 'int'> <class 'int'> True <class 'float'> <class 'float'> True <class 'str'> <class 'str'> True <class 'list'> <class 'list'> True <class 'tuple'> <class 'tuple'> True <class 'set'> <class 'set'> True <class 'dict'> <class 'dict'> True <class 'complex'> <class 'complex'> True <class 'bool'> <class 'bool'> True <class 'function'> <class 'function'> True <class '__main__.k'> <class '__main__.k'> True

注意到在type类针对实例kk使用时，实际上返回了其类名k，因此甚至可以使用返回值再次实例化一个对象，如下例5所示。

# 例5 class k: pass kk=k() kkk=type(kk)() # type(kk)相当于k

如果对类名再次使用type，返回的会是type类，因为所有的类都是type这个元类的实例，如下例6所示。

# 例6 class k: pass kk=k() print(type(type(kk))) print(isinstance(type(kk), type)) # 检测自定义类是否是type类或其父类的实例 # 输出 <class 'type'> True

总结来说就是，object类直接或间接是所有类的父类（可以用issubclass函数检测），而所有类又都是type类的实例（可以用isinstance函数检测）。