Python3：为什么 __spec__ 有效？
Python3: Why does __spec__ work?
变量__spec__从何而来？
$ brew install python3
$ python3
Python 3.4.2 (default, Jan 5 2015, 11:57:21)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.56)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
# Under Python 2.7.x this gives a NameError
>>> None is __spec__
True
来自 the Python Language Reference, Part 5: The Import System（强调我的）：
The __spec__ attribute must be set to the module spec that was used when importing the module. This is used primarily for introspection and during reloading. Setting __spec__ appropriately applies equally to modules initialized during interpreter startup. The one exception is __main__, where __spec__ is set to None in some cases.
New in version 3.4.
根据 Python 3 docs，如果您使用交互式提示，__spec__ 总是 None：
When Python is started with the -m option, __spec__ is set to the
module spec of the corresponding module or package. __spec__ is also
populated when the __main__ module is loaded as part of executing a
directory, zipfile or other sys.path entry.
In the remaining cases __main__.__spec__ is set to None, as the code
used to populate the __main__ does not correspond directly with an
importable module:
- interactive prompt
- -c switch
- running from stdin
- running directly from a source or bytecode file
变量__spec__从何而来？
$ brew install python3
$ python3
Python 3.4.2 (default, Jan 5 2015, 11:57:21)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.56)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
# Under Python 2.7.x this gives a NameError
>>> None is __spec__
True
来自 the Python Language Reference, Part 5: The Import System（强调我的）：
The
__spec__attribute must be set to the module spec that was used when importing the module. This is used primarily for introspection and during reloading. Setting__spec__appropriately applies equally to modules initialized during interpreter startup. The one exception is__main__, where__spec__is set to None in some cases.New in version 3.4.
根据 Python 3 docs，如果您使用交互式提示，__spec__ 总是 None：
When Python is started with the -m option,
__spec__is set to the module spec of the corresponding module or package.__spec__is also populated when the__main__module is loaded as part of executing a directory, zipfile or other sys.path entry.In the remaining cases
__main__.__spec__is set to None, as the code used to populate the__main__does not correspond directly with an importable module:
- interactive prompt
- -c switch
- running from stdin
- running directly from a source or bytecode file