Question

我想动态声明一个函数，我希望包含对全局变量的任何访问或者定义哪些变量是空闲的，并包装对自由变量的任何访问。

我正在玩这样的代码：

class D:
    def __init__(self):
        self.d = {}     
    def __getitem__(self, k):
        print "D get", k
        return self.d[k]
    def __setitem__(self, k, v):
        print "D set", k, v
        self.d[k] = v
    def __getattr__(self, k):
        print "D attr", k
        raise AttributeError

globalsDict = D()

src = "def foo(): print x"

compiled = compile(src, "<foo>", "exec")
exec compiled in {}, globalsDict

f = globalsDict["foo"]
print(f)

f()

这会产生输出：

D set foo <function foo at 0x10f47b758>
D get foo
<function foo at 0x10f47b758>
Traceback (most recent call last):
  File "test_eval.py", line 40, in <module>
    f()
  File "<foo>", line 1, in foo
NameError: global name 'x' is not defined

我想要的是以某种方式使用类似dict的包装器x来捕获对D的访问权限。我怎么能这样做？

我不想预定义所有全局变量（在本例中为x），因为我希望能够懒得加载它们。

Answer 1

您正在寻找的是对象代理。

这是一个支持预调用和后调用挂钩的对象代理的配方：

http://code.activestate.com/recipes/366254-generic-proxy-object-with-beforeafter-method-hooks/

创建一个实际上不加载对象的子类，直到第一次调用_pre挂钩为止。访问该对象的任何内容都将导致加载真实对象，并且所有调用似乎都将由真实对象直接处理。

Answer 2

试试这个

class GlobalDict(object):

    def __init__(self, **kwargs):
        self.d = kwargs

    def __getitem__(self, key):
        print 'getting', key
        return self.d[key]

    def __setitem__(self, key, value):
        print 'setting', key, 'to', value
        if hasattr(value, '__globals__'):
            value.__globals__.update(self.d)
        self.d[key] = value
        for v in self.d.values():
            if v is not value:
                if hasattr(v, '__globals__'):
                    v.__globals__.update(self.d)

    def __delitem__(self, key):
        print 'deling', key
        del self.d[key]
        for v in self.d.values():
            if hasattr(v, '__globals__'):
                del v.__globals__[key]

>>> gd = GlobalDict()
>>> src = 'def foo(): print x'
>>> compiled = compile(src, '<foo>', 'exec')
>>> exec compiled in {}, gd
setting foo to <function foo at 0x102223b18>
>>> f = gd['foo']
getting foo
>>> f
<function foo at 0x102223b18>
>>> f() # This one will throw an error
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "<foo>", line 1, in foo
NameError: global name 'x' is not defined
>>> gd['x'] = 1
setting x to 1
>>> f()
1
>>> del gd['x'] # removes 'x' from the globals of anything in gd
>>> f() # Will now fail again
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "<foo>", line 1, in foo
NameError: global name 'x' is not defined

Python：如何动态设置函数闭包环境

2 个答案: