`import somemodule` does not check all paths in `sys.path`

[MRAB]

On 2018-07-28 22:16, stefand986 at gmail.com wrote:
> Hi everyone,
> I am currently investigating an interesting bug in homeassistant which is a bit hard to reproduce. I already dug so deep that I ask here, because I think the root cause has to do with how Python locates and loads modules/packages.
> 
> The "story" is: In homeassistant (short HA) some modules are installed at runtime during first start ("bootstrapping"), and for some reason loading the modules fails directly after installing the modules. Subsequent starts work fine.
> 
> The modules that are installed during bootstrapping are installed to `~/.homeassistant/deps/lib/python3.7/site-packages`. Installing the modules happens in a different thread than where the modules are imported. (However as far as I can tell the importing thread waits for the install to finish.)
> 
> Now the interesting thing is that when I start HA in verbose mode, I can see that Python is trying not all of the paths that are in `sys.path` (in the following snippet I cut out some stuff for brevity. Link to the full log at the end). As one can see the `~/.homeassistant/deps/lib/python3.7/site-packages` location is not tried and hence the import fails:
> 
>    ```
>    # trying /home/pyuser/.homeassistant/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    # trying /home/pyuser/.homeassistant/sqlalchemy.abi3.so
>    # trying /home/pyuser/.homeassistant/sqlalchemy.so
>    # trying /home/pyuser/.homeassistant/sqlalchemy.py
>    # trying /home/pyuser/.homeassistant/sqlalchemy.pyc
>    # trying /home/pyuser/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    [...]
>    # trying /usr/local/lib/python3.7/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    [...]
>    # trying /usr/local/lib/python3.7/lib-dynload/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    [...]
>    # trying /home/pyuser/.local/lib/python3.7/site-packages/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    [...]
>    # trying /usr/local/lib/python3.7/site-packages/sqlalchemy.cpython-37m-x86_64-linux-gnu.so
>    [...]
>    Exception in thread Recorder:
>    Traceback (most recent call last):
>      File "/usr/local/lib/python3.7/threading.py", line 917, in _bootstrap_inner
>        self.run()
>      File "/home/pyuser/.local/lib/python3.7/site-packages/homeassistant/components/recorder/__init__.py", line 187, in run
>        from .models import States, Events
>      File "<frozen importlib._bootstrap>", line 983, in _find_and_load
>      File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
>      File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
>      File "<frozen importlib._bootstrap_external>", line 728, in exec_module
>      File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
>      File "/home/pyuser/.local/lib/python3.7/site-packages/homeassistant/components/recorder/models.py", line 8, in <module>
>        from sqlalchemy import (
>      File "<frozen importlib._bootstrap>", line 983, in _find_and_load
>      File "<frozen importlib._bootstrap>", line 965, in _find_and_load_unlocked
>    ModuleNotFoundError: No module named 'sqlalchemy'
>    ```
> 
> I also checked that this path is also really in `sys.path` at the time the import happens. This is `sys.path` printed out directly before the `import sqlalchemy statement`:
> 
>    ```
>    ['/home/pyuser/.homeassistant',
>     '/home/pyuser/.homeassistant/deps/lib/python3.7/site-packages',
>     '/home/pyuser',
>     '/usr/local/lib/python37.zip',
>     '/usr/local/lib/python3.7',
>     '/usr/local/lib/python3.7/lib-dynload',
>     '/home/pyuser/.local/lib/python3.7/site-packages',
>     '/usr/local/lib/python3.7/site-packages']
>    ```
> 
> 
> What I already tried is to do a importlib.invalidate_caches() after installing the modules. However this does not fix it.
> 
> So what is happening here? Why does the import skip `~/.homeassistant/deps/lib/python3.7/site-packages`? Any tips on how I can investigate further?
> 
> Link to the full log: https://gist.github.com/StefanD986/fbf08426ceaad657929b973cd5add25a#file-homeassistant_verbose_first_start-txt-L5787
> 
The log contains entries that say "Please check your config". To me it 
looks like it hasn't been installed.

Does the path 
/home/pyuser/.homeassistant/deps/lib/python3.7/site-packages actually exist?