Packages in same namespace: can't import module in setup script

Question

I'm curious about the following situation. Let's say I have two projects named project_alpha and project_bravo , both defining a top-level namespace package mymeta . The layout:

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__.py s contain only the line __import__('pkg_resources').declare_namespace(__name__) (according to namespace section in setuptools docs ). Contents of both version.py s:

__version_info__ = (0, 9, 9, 'dev0')
__version__ = '.'.join((str(entry) for entry in __version_info__)) 

The setup.py script for project_alpha is pretty simple. The namespace package mymeta is declared, and the version is taken from the version module:

# 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 script for project_bravo has the same structure, but with a twist: project_bravo depends on project_alpha when building:

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(),
)

When building project_bravo , I get the following error:

~/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'

Unfortunately, I don't understand the error here. It has something to do with the imports order, right? If I comment out the import of mymeta.project_bravo.version in project_bravo/setup.py and replace the version with some hard-coded string, suddenly the build succeeds...

---

Edit: I introduced a workaround for this issue. Instead of trying to import the version directly, I exec the version module to avoid the import problems. Of course, this is not a proper solution, thus not posting this as answer, but still here it is:

__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())

After the version script is read and executed, the version is initialized, thus no need to import anything from mymeta package.

Answer 1

As mentioned in the comments: The command

$ python setup.py sdist

for mymeta.project_bravo downloads an egg of mymeta.project_alpha from a private pypi repo.

Namespace packages are very delicate concerning their imports.

eg I found out that when I install ns.a and ns.b regularly in my environment and supply the import path of ns.d in a .pth file in the site-packages directory, it will not work, no matter what. However when I symlink to ns.d in site-packeges/ns directory it will work.

If I install none of the components and supply all paths in a .pth in the site-packages directory, everything works fine.

If I install all of the components regularly also everything works fine.

Just when I mix concepts it will not work.

Therefore I suspect that this might also be the issue here: Different strategies for the import paths.

You might want to try to modify your __init__.py file to:

from pkgutil import extend_path

__path__ = extend_path(__path__, __name__)
__import__('pkg_resources').declare_namespace(__name__)

I regret my decision to do namespace packages. I would never do it again.

Answer 2

Almost one year later, I once again faced this issue and the solution for python>=3.3 is to use implicit namespace packages as specified in PEP 420 . The project structure is barely changed, just both the __init__.py s for pkgutil-style namespace package mymeta are gone:

project_alpha/
   -> mymeta/
        -> project_alpha/
             -> __init__.py
             -> version.py
   -> setup.py

project_bravo/
   -> mymeta/
        -> project_bravo/
             -> __init__.py
             -> version.py
   -> setup.py

To make setuptools happy, both setup scripts need to be adjusted as well:

...
setup(
    ...
    packages=['mymeta.' + pkg for pkg in find_packages('mymeta')],
)

Now the imports will be resolved correctly when building project-bravo .