[英]Why are modules that haven't been imported in 'sys.modules' in Python 3?
I was reading how to check if a python module has been imported and the instructions seems clear, check for the module in the sys.modules
. 我正在阅读如何检查是否已导入python模块 ,并且说明似乎很清楚,请在
sys.modules
检查该模块。 This works as I expected in Python 2, but not with Python 3 (3.5 and 3.6 tested). 这可以按我在Python 2中预期的方式工作,但不适用于Python 3(已测试3.5和3.6)。 For example:
例如:
Python 3.6 Python 3.6
>>> import sys
>>> 'itertools' in sys.modules
True
Python 2.7 Python 2.7
>>> import sys
>>> 'itertools' in sys.modules
False
I note that, itertools
is described as a 'built-in' in the Python 3 sys.modules dict
( <module 'itertools' (built-in)>
), and not in Python 2 so maybe that's why it's in sys.modules
prior to being imported, but it's not listed as a built-in . 我注意到,
itertools
在Python 3 sys.modules dict
( <module 'itertools' (built-in)>
)中被描述为“内置”,而不是在Python 2中,所以也许这就是它在sys.modules
中的原因在导入之前,但未作为内置项列出 。 Anyway, since itertools
still needs importing in Python 3, I'd be grateful for an explanation. 无论如何,由于
itertools
仍然需要在Python 3中导入,因此我很感谢您提供一个解释。
They have been imported, just not by you. 它们已被导入,只是不是您导入的。 Exactly what parts of interpreter startup caused the module to be loaded are unimportant implementation details, but you can trace possible paths if you want.
解释器启动的确切原因是导致模块加载的是不重要的实现详细信息,但是您可以根据需要跟踪可能的路径。 For example,
itertools
is imported by reprlib
例如,
itertools
由reprlib
导入
from itertools import islice
which is imported by functools
: 这是由
functools
导入的:
from reprlib import recursive_repr
which is imported by types
: 通过
types
导入:
import functools as _functools
which is imported by importlib
: 这是由
importlib
导入的:
import types
which is bootstrapped at interpreter startup because it's where most of the implementation of importing is. 它在解释器启动时被引导,因为它是大多数导入实现的地方。
It appears that in Python 3, the itertools extension is actually compiled into the main Python binary unlike Python 2. If you do a 看来在Python 3中,itertools扩展实际上是编译为Python 2中的主要二进制文件,这与Python 2不同。
import sys
and then a 然后一个
'itertools' in sys.builtin_module_names
>> True
it is clear. 很明显。 Doing the exact same steps in a Python 2.x console results in a
False
. 在Python 2.x控制台中执行完全相同的步骤会导致
False
。
As per the docs , builtin_module_names
comprises of 'modules that are compiled into this Python interpreter' . 根据文档 ,
builtin_module_names
包含“已编译到此Python解释器中的模块” 。
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