[英]Why can't I access builtins if I use a custom dict as a function's globals?
I have a dict
subclass like this: 我有一个像这样的dict
子类:
class MyDict(dict):
def __getitem__(self, name):
return globals()[name]
This class can be used with eval
and exec
without issues: 这个类可以与eval
和exec
一起使用而不会出现问题:
>>> eval('bytearray', MyDict())
<class 'bytearray'>
>>> exec('print(bytearray)', MyDict())
<class 'bytearray'>
But if I instantiate a function object with the types.FunctionType
constructor, the function can't access any builtins: 但是如果我使用types.FunctionType
构造函数实例化一个函数对象,则该函数无法访问任何内置函数:
import types
func = lambda: bytearray
func_copy = types.FunctionType(func.__code__,
MyDict(),
func.__name__,
func.__defaults__,
func.__closure__)
print(func_copy())
# Traceback (most recent call last):
# File "untitled.py", line 16, in <module>
# print(func_copy())
# File "untitled.py", line 8, in <lambda>
# func = lambda: bytearray
# NameError: name 'bytearray' is not defined
Replacing MyDict()
with globals()
or dict(globals())
or event {'__builtins__': __builtins__}
makes the code print <class 'bytearray'>
as expected. 用globals()
或dict(globals())
或event {'__builtins__': __builtins__}
替换MyDict()
会使代码按预期打印<class 'bytearray'>
。
I don't understand where this exception is coming from. 我不明白这个例外的来源。 Can anyone explain this behavior? 谁能解释这种行为? Why does it work with eval
but not with a function object? 为什么它与eval
但不与函数对象一起使用?
Not a complete answer, but what seems to be happening is that CPython ignores the custom __getitem__
when it accesses the builtins. 不是一个完整的答案,但似乎正在发生的是CPython在访问内置函数时忽略了自定义__getitem__
。 It seems to treat MyDict
like a normal (not subclassed) dict. 它似乎将MyDict
视为正常( MyDict
类)dict。 If the '__builtins__'
key is actually present in the dict, then everything works correctly: 如果'__builtins__'
键实际存在于dict中,那么一切正常:
class MyDict(dict):
def __getitem__(self, name):
return globals()[name]
import types
globs = MyDict()
globs['__builtins__'] = __builtins__
func = lambda: bytearray
func_copy = types.FunctionType(func.__code__,
globs,
func.__name__,
func.__defaults__,
func.__closure__)
print(func_copy())
# output: <class 'bytearray'>
The question remains why this only happens with FunctionType
, and not with eval
and exec
. 问题仍然是为什么这只发生在FunctionType
,而不是发生在eval
和exec
。
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