我很好奇下面的情况。假设我有两个名为project_alpha and project_bravo，都定义了顶级命名空间包mymeta。布局：
project_alpha/
-> mymeta/
-> __init__.py
-> project_alpha/
-> __init__.py
-> version.py
-> setup.py
project_bravo/
-> mymeta/
-> __init__.py
-> project_bravo/
-> __init__.py
-> version.py
-> setup.py
Both mymeta/__init__.pys 仅包含行__import__('pkg_resources').declare_namespace(__name__)（根据setuptools 文档中的命名空间部分 http://setuptools.readthedocs.io/en/latest/setuptools.html#namespace-packages）。两者的内容version.pys:
__version_info__ = (0, 9, 9, 'dev0')
__version__ = '.'.join((str(entry) for entry in __version_info__))
The setup.py脚本为project_alpha很简单。命名空间包mymeta被声明，并且版本取自version模块：
# project_alpha
from setuptools import find_packages, setup
from mymeta.project_alpha.version import __version__
setup(
name='mymeta.project-alpha',
version=__version__,
namespace_packages=['mymeta'],
packages=find_packages(),
)
The setup.py脚本为project_bravo具有相同的结构，但有所不同：project_bravo依赖于取决于project_alpha构建时：
from setuptools import find_packages, setup
from mymeta.project_bravo.version import __version__
setup(
name='mymeta.project-bravo',
version=__version__,
namespace_packages=['mymeta'],
setup_requires=['mymeta.project-alpha'],
packages=find_packages(),
)
建造时project_bravo，我收到以下错误：
~/project_bravo $ python setup.py sdist
Traceback (most recent call last):
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 156, in save_modules
yield saved
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 197, in setup_context
yield
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 246, in run_setup
DirectorySandbox(setup_dir).run(runner)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 276, in run
return func()
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 245, in runner
_execfile(setup_script, ns)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 47, in _execfile
exec(code, globals, locals)
File "/tmp/easy_install-ahmxos98/mymeta.project-alpha-0.9.9.dev0/setup.py", line 6, in <module>
try:
ImportError: No module named 'mymeta.project_alpha'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "setup.py", line 22, in <module>
packages=find_packages(),
File "/usr/lib64/python3.5/distutils/core.py", line 108, in setup
_setup_distribution = dist = klass(attrs)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/dist.py", line 315, in __init__
self.fetch_build_eggs(attrs['setup_requires'])
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/dist.py", line 361, in fetch_build_eggs
replace_conflicting=True,
File "/tmp/tstenv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 853, in resolve
dist = best[req.key] = env.best_match(req, ws, installer)
File "/tmp/tstenv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1125, in best_match
return self.obtain(req, installer)
File "/tmp/tstenv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1137, in obtain
return installer(requirement)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/dist.py", line 429, in fetch_build_egg
return cmd.easy_install(req)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 665, in easy_install
return self.install_item(spec, dist.location, tmpdir, deps)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 695, in install_item
dists = self.install_eggs(spec, download, tmpdir)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 876, in install_eggs
return self.build_and_install(setup_script, setup_base)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 1115, in build_and_install
self.run_setup(setup_script, setup_base, args)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 1101, in run_setup
run_setup(setup_script, args)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 249, in run_setup
raise
File "/usr/lib64/python3.5/contextlib.py", line 77, in __exit__
self.gen.throw(type, value, traceback)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 197, in setup_context
yield
File "/usr/lib64/python3.5/contextlib.py", line 77, in __exit__
self.gen.throw(type, value, traceback)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 168, in save_modules
saved_exc.resume()
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 143, in resume
six.reraise(type, exc, self._tb)
File "/tmp/tstenv/lib/python3.5/site-packages/pkg_resources/_vendor/six.py", line 685, in reraise
raise value.with_traceback(tb)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 156, in save_modules
yield saved
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 197, in setup_context
yield
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 246, in run_setup
DirectorySandbox(setup_dir).run(runner)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 276, in run
return func()
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 245, in runner
_execfile(setup_script, ns)
File "/tmp/tstenv/lib/python3.5/site-packages/setuptools/sandbox.py", line 47, in _execfile
exec(code, globals, locals)
File "/tmp/easy_install-ahmxos98/mymeta.project-alpha-0.9.9.dev0/setup.py", line 6, in <module>
try:
ImportError: No module named 'mymeta.project_alpha'
不幸的是，我不明白这里的错误。跟进口订单有关系吧？如果我注释掉导入mymeta.project_bravo.version in project_bravo/setup.py并替换version使用一些硬编码的字符串，突然构建成功了......
编辑：我介绍了此问题的解决方法。我没有尝试直接导入版本，而是exec版本模块以避免导入问题。当然，这不是一个正确的解决方案，因此不会将其发布为答案，但仍然在这里：
__version__ = None # if the exec fails, leave the version unset, the resulting build version will be 0.0.0
version_script_path = os.path.relpath(os.path.join(os.path.dirname(__file__), 'mymeta', 'project_alpha', 'version.py'))
with open(version_script_path) as version_script:
exec(version_script.read())
读取并执行版本脚本后，版本将被初始化，因此无需从其中导入任何内容mymeta包裹。
