Python 如何制作;“仅关键字”;有数据类的字段?
支持仅生成参数关键字:Python 如何制作;“仅关键字”;有数据类的字段?,python,keyword-argument,python-3.7,python-dataclasses,Python,Keyword Argument,Python 3.7,Python Dataclasses,支持仅生成参数关键字: class S3Obj: def __init__(self, bucket, key, *, storage_class='Standard'): self.bucket = bucket self.key = key self.storage_class = storage_class 如何使用计算机获取这种签名?类似于此,但最好不使用SyntaxError: @dataclass class S3Obj:
class S3Obj:
def __init__(self, bucket, key, *, storage_class='Standard'):
self.bucket = bucket
self.key = key
self.storage_class = storage_class
如何使用计算机获取这种签名?类似于此,但最好不使用SyntaxError
:
@dataclass
class S3Obj:
bucket: str
key: str
*
storage_class: str = 'Standard'
理想情况下是声明式的,但是使用\uuuu post\u init\uuuu
钩子和/或替换类装饰器也可以,只要代码是可重用的
编辑:可能类似于这种语法,使用省略号文字
@mydataclass
class S3Obj:
bucket: str
key: str
...
storage_class: str = 'Standard'
这样做时,您不会从
dataclasses
获得太多帮助。没有办法说字段应该只由关键字参数初始化,\uuuu post\u init\uuu
钩子不知道原始构造函数参数是否由关键字传递。此外,没有好的方法来内省InitVar
s,更不用说将InitVar
s标记为关键字了
至少,您必须替换生成的\uuuu init\uuuu
。可能最简单的方法就是手工定义\uuuuu init\uuuu
。如果您不想这样做,最可靠的方法可能是创建字段对象并在元数据中标记它们,然后在您自己的decorator中检查元数据。这比听起来还要复杂:
import dataclasses
import functools
import inspect
# Helper to make calling field() less verbose
def kwonly(default=dataclasses.MISSING, **kwargs):
kwargs.setdefault('metadata', {})
kwargs['metadata']['kwonly'] = True
return dataclasses.field(default=default, **kwargs)
def mydataclass(_cls, *, init=True, **kwargs):
if _cls is None:
return functools.partial(mydataclass, **kwargs)
no_generated_init = (not init or '__init__' in _cls.__dict__)
_cls = dataclasses.dataclass(_cls, **kwargs)
if no_generated_init:
# No generated __init__. The user will have to provide __init__,
# and they probably already have. We assume their __init__ does
# what they want.
return _cls
fields = dataclasses.fields(_cls)
if any(field.metadata.get('kwonly') and not field.init for field in fields):
raise TypeError('Non-init field marked kwonly')
# From this point on, ignore non-init fields - but we don't know
# about InitVars yet.
init_fields = [field for field in fields if field.init]
for i, field in enumerate(init_fields):
if field.metadata.get('kwonly'):
first_kwonly = field.name
num_kwonly = len(init_fields) - i
break
else:
# No kwonly fields. Why were we called? Assume there was a reason.
return _cls
if not all(field.metadata.get('kwonly') for field in init_fields[-num_kwonly:]):
raise TypeError('non-kwonly init fields following kwonly fields')
required_kwonly = [field.name for field in init_fields[-num_kwonly:]
if field.default is field.default_factory is dataclasses.MISSING]
original_init = _cls.__init__
# Time to handle InitVars. This is going to get ugly.
# InitVars don't show up in fields(). They show up in __annotations__,
# but the current dataclasses implementation doesn't understand string
# annotations, and we want an implementation that's robust against
# changes in string annotation handling.
# We could inspect __post_init__, except there doesn't have to be a
# __post_init__. (It'd be weird to use InitVars with no __post_init__,
# but it's allowed.)
# As far as I can tell, that leaves inspecting __init__ parameters as
# the only option.
init_params = tuple(inspect.signature(original_init).parameters)
if init_params[-num_kwonly] != first_kwonly:
# InitVars following kwonly fields. We could adopt a convention like
# "InitVars after kwonly are kwonly" - in fact, we could have adopted
# "all fields after kwonly are kwonly" too - but it seems too likely
# to cause confusion with inheritance.
raise TypeError('InitVars after kwonly fields.')
# -1 to exclude self from this count.
max_positional = len(init_params) - num_kwonly - 1
@functools.wraps(original_init)
def __init__(self, *args, **kwargs):
if len(args) > max_positional:
raise TypeError('Too many positional arguments')
check_required_kwargs(kwargs, required_kwonly)
return original_init(self, *args, **kwargs)
_cls.__init__ = __init__
return _cls
def check_required_kwargs(kwargs, required):
# Not strictly necessary, but if we don't do this, error messages for
# required kwonly args will list them as positional instead of
# keyword-only.
missing = [name for name in required if name not in kwargs]
if not missing:
return
# We don't bother to exactly match the built-in logic's exception
raise TypeError(f"__init__ missing required keyword-only argument(s): {missing}")
用法示例:
@mydataclass
class S3Obj:
bucket: str
key: str
storage_class: str = kwonly('Standard')
这是经过一些测试的,但不像我希望的那样彻底
您无法使用..
获得您建议的语法,因为..
不会做元类或装饰程序可以看到的任何事情。您可以获得一些非常接近于实际触发名称查找或赋值的东西,比如kwonly\u start=True
,这样元类就可以看到它的发生。然而,这方面的健壮实现编写起来很复杂,因为有很多事情需要专门处理。继承、typing.ClassVar
、dataclasses.InitVar
、注释中的转发引用等,如果不小心处理,都会导致问题。继承可能会导致最多的问题
无法处理所有精细位的概念验证可能如下所示:
# Does not handle inheritance, InitVar, ClassVar, or anything else
# I'm forgetting.
class POCMetaDict(dict):
def __setitem__(self, key, item):
# __setitem__ instead of __getitem__ because __getitem__ is
# easier to trigger by accident.
if key == 'kwonly_start':
self['__non_kwonly'] = len(self['__annotations__'])
super().__setitem__(key, item)
class POCMeta(type):
@classmethod
def __prepare__(cls, name, bases, **kwargs):
return POCMetaDict()
def __new__(cls, name, bases, classdict, **kwargs):
classdict.pop('kwonly_start')
non_kwonly = classdict.pop('__non_kwonly')
newcls = super().__new__(cls, name, bases, classdict, **kwargs)
newcls = dataclass(newcls)
if non_kwonly is None:
return newcls
original_init = newcls.__init__
@functools.wraps(original_init)
def __init__(self, *args, **kwargs):
if len(args) > non_kwonly:
raise TypeError('Too many positional arguments')
return original_init(self, *args, **kwargs)
newcls.__init__ = __init__
return newcls
你会像这样使用它
class S3Obj(metaclass=POCMeta):
bucket: str
key: str
kwonly_start = True
storage_class: str = 'Standard'
这是未经测试的。我想知道为什么这不是dataclass API的一部分,这对我来说很重要
如果所有的参数都是关键字参数,可能会简单一点,下面的内容就足够了
从数据类导入数据类
从functools导入包装
仅限def kwargs_(cls):
@包装(cls)
def呼叫(**kwargs):
返回cls(**kwargs)
回电
@仅kwargs_
@数据类
类坐标:
纬度:浮点=0
经度:float=0
这并不完美,因为使用位置参数时出现的错误引用了call
:
--------------------------------------------------------
TypeError回溯(最近一次调用上次)
在里面
---->1c=坐标(1,经度=2)
2帮助(c)
TypeError:call()接受0个位置参数,但给出了1个
类似地,dataclass的构造函数文档已经过时,并且没有反映新的约束
如果只有一些关键字字段,可能是这个
def kwargs(*关键字):
def装饰器(cls):
@包装(cls)
def调用(*args,**kwargs):
如果有(千瓦不以千瓦为单位,而千瓦以关键字为单位):
raise TypeError(f“{cls.\uuuuuu name\uuuuuu}.\uuuuu init\uuuuuuuu()需要{keywords}作为关键字参数”)
返回cls(*args,**kwargs)
回电
返回装饰器
@kwargs(“经度”)
@数据类(冻结=真)
类坐标:
纬度:浮动
经度:float=0
..
不会执行任何其他代码可以看到的操作。