在 Python 中进行自动属性分配的最佳方法是什么，这是一个好主意吗? [英] What is the best way to do automatic attribute assignment in Python, and is it a good idea?

问题描述

而不是每次定义类时都编写这样的代码:

Instead of writing code like this every time I define a class:

class Foo(object): 
     def __init__(self, a, b, c, d, e, f, g):
        self.a = a
        self.b = b
        self.c = c
        self.d = d
        self.e = e
        self.f = f
        self.g = g

我可以使用这个自动属性分配方法.

class Foo(object):
     @autoassign
     def __init__(self, a, b, c, d, e, f, g):
        pass

两个问题:

1. 是否存在与此快捷方式相关的缺点或陷阱?
2. 有没有更好的方法来实现类似的便利?

推荐答案

关于自动分配代码的一些问题让我感到困惑(主要是风格，但还有一个更严重的问题):

There are some things about the autoassign code that bug me (mostly stylistic, but one more serious problem):

1. autoassign 不分配'args' 属性:

1. autoassign does not assign an 'args' attribute:

class Foo(object):
    @autoassign
    def __init__(self,a,b,c=False,*args):
        pass
a=Foo('IBM','/tmp',True, 100, 101)
print(a.args)
# AttributeError: 'Foo' object has no attribute 'args'

autoassign 就像一个装饰器.但是 autoassign(*argnames) 调用返回装饰器的函数.为了实现这个魔力，autoassign需要先测试它的类型争论.如果可以选择，我喜欢功能而不是测试其参数的类型.

autoassign acts like a decorator. But autoassign(*argnames) calls a function which returns a decorator. To achieve this magic, autoassign needs to test the type of its first argument. If given a choice, I prefer functions not test the type of its arguments.

好像有很多用于设置的代码量筛子，lambdas中的lambdas，ifilters，还有很多条件.

There seems to be a considerable amount of code devoted to setting up sieve, lambdas within lambdas, ifilters, and lots of conditions.

if kwargs:
    exclude, f = set(kwargs['exclude']), None
    sieve = lambda l:itertools.ifilter(lambda nv: nv[0] not in exclude, l)
elif len(names) == 1 and inspect.isfunction(names[0]):
    f = names[0]
    sieve = lambda l:l
else:
    names, f = set(names), None
    sieve = lambda l: itertools.ifilter(lambda nv: nv[0] in names, l)

我认为可能有更简单的方法.(看下面).

I think there might be a simpler way. (See below).

for _ initertools.starmap(assigned.setdefault,默认值):通过.我不认为map 或 starmap 旨在调用函数，其唯一目的是它们的副作用.本来可以用平凡写得更清楚:

for _ in itertools.starmap(assigned.setdefault, defaults): pass. I don't think map or starmap was meant to call functions, whose only purpose is their side effects. It could have been written more clearly with the mundane:

for key,value in defaults.iteritems():
    assigned.setdefault(key,value)

这是一个替代的更简单的实现，它具有与自动分配相同的功能(例如，可以包含和排除)，并且解决了上述问题:

Here is an alternative simpler implementation which has the same functionality as autoassign (e.g. can do includes and excludes), and which addresses the above points:

import inspect
import functools

def autoargs(*include, **kwargs):
    def _autoargs(func):
        attrs, varargs, varkw, defaults = inspect.getargspec(func)

        def sieve(attr):
            if kwargs and attr in kwargs['exclude']:
                return False
            if not include or attr in include:
                return True
            else:
                return False

        @functools.wraps(func)
        def wrapper(self, *args, **kwargs):
            # handle default values
            if defaults:
                for attr, val in zip(reversed(attrs), reversed(defaults)):
                    if sieve(attr):
                        setattr(self, attr, val)
            # handle positional arguments
            positional_attrs = attrs[1:]
            for attr, val in zip(positional_attrs, args):
                if sieve(attr):
                    setattr(self, attr, val)
            # handle varargs
            if varargs:
                remaining_args = args[len(positional_attrs):]
                if sieve(varargs):
                    setattr(self, varargs, remaining_args)
            # handle varkw
            if kwargs:
                for attr, val in kwargs.items():
                    if sieve(attr):
                        setattr(self, attr, val)
            return func(self, *args, **kwargs)
        return wrapper
    return _autoargs

这是我用来检查其行为的单元测试:

And here is the unit test I used to check its behavior:

import sys
import unittest
import utils_method as um

class Test(unittest.TestCase):
    def test_autoargs(self):
        class A(object):
            @um.autoargs()
            def __init__(self,foo,path,debug=False):
                pass
        a=A('rhubarb','pie',debug=True)
        self.assertTrue(a.foo=='rhubarb')
        self.assertTrue(a.path=='pie')
        self.assertTrue(a.debug==True)

        class B(object):
            @um.autoargs()
            def __init__(self,foo,path,debug=False,*args):
                pass
        a=B('rhubarb','pie',True, 100, 101)
        self.assertTrue(a.foo=='rhubarb')
        self.assertTrue(a.path=='pie')
        self.assertTrue(a.debug==True)
        self.assertTrue(a.args==(100,101))        

        class C(object):
            @um.autoargs()
            def __init__(self,foo,path,debug=False,*args,**kw):
                pass
        a=C('rhubarb','pie',True, 100, 101,verbose=True)
        self.assertTrue(a.foo=='rhubarb')
        self.assertTrue(a.path=='pie')
        self.assertTrue(a.debug==True)
        self.assertTrue(a.verbose==True)        
        self.assertTrue(a.args==(100,101))        

    def test_autoargs_names(self):
        class C(object):
            @um.autoargs('bar','baz','verbose')
            def __init__(self,foo,bar,baz,verbose=False):
                pass
        a=C('rhubarb','pie',1)
        self.assertTrue(a.bar=='pie')
        self.assertTrue(a.baz==1)
        self.assertTrue(a.verbose==False)
        self.assertRaises(AttributeError,getattr,a,'foo')

    def test_autoargs_exclude(self):
        class C(object):
            @um.autoargs(exclude=('bar','baz','verbose'))
            def __init__(self,foo,bar,baz,verbose=False):
                pass
        a=C('rhubarb','pie',1)
        self.assertTrue(a.foo=='rhubarb')
        self.assertRaises(AttributeError,getattr,a,'bar')

    def test_defaults_none(self):
        class A(object):
            @um.autoargs()
            def __init__(self,foo,path,debug):
                pass
        a=A('rhubarb','pie',debug=True)
        self.assertTrue(a.foo=='rhubarb')
        self.assertTrue(a.path=='pie')
        self.assertTrue(a.debug==True)


if __name__ == '__main__':
    unittest.main(argv = sys.argv + ['--verbose'])

PS.使用 autoassign 或 autoargs 与 IPython 代码完成兼容.

PS. Using autoassign or autoargs is compatible with IPython code completion.

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