问为什么不可能导入一些python子模块？

EN

from importlib import import_module
from pkgutil import walk_packages
import sys
import operator


def get_attr(module, attr):
    return operator.attrgetter(attr.split('.', 1)[1])(module)


def isimported(module_name):
    return module_name in sys.modules


def get_submodules(module_name):
    submodules = {}
    module = import_module(module_name)
    for loader, name, is_pkg in walk_packages(module.__path__, module.__name__ + '.'):
        if isimported(name):
            submodules[name] = get_attr(module, name)
        else:
            try:
                submodules[name] = __import__(name)
            except ImportError:
                pass

if __name__ == "__main__":
    get_submodules('numpy')