Werkzeug: Reloader, python -m, and sys.path

I don't think it would not harm if Werkzeug spawned the subprocess with actually the same arguments, using __loader__.fullname in Python 2 and __loader__.name in Python 3 if existent.

@untitaker, I don’t understand what you mean. What’s __loader__?

Can we detect in Python if python -m somemodule was used or not?

I camne across a StackOverflow answer that explained how to get the current module name. A simple test shows that in Python 2, __loader__.fullname is available:

print(__loader__.fullname)

The __loader__ global doesn't exist if the Python file is executed without -m, and it also doesn't exist in imported modules.

In Python 3, both the module executed with -m and any other imported modules seem to have a __loader__ global, the fullname attribute is now name. But inside every module, the name attribute has the value of the _current_ module.

So, in Python 2 we _can_ detect if we're running with -m, but not in 3.

Also the detection is very limited either, so you only can detect inside the directly executed module if python -m was used by checking for the __loader__ variable. Also, this behavior seems sparsely documented, so i am not sure if that's what we want in Werkzeug anyway.

I just came across this bug myself. I expected the -m flag to be present in sys.argv, but it most definitely isn't.

Is there any kind of workaround for this?

Yes, one is presented in https://github.com/mitsuhiko/flask/issues/1246

On 9 July 2015 15:08:30 CEST, Wayne Werner [email protected] wrote:

I just came across this bug myself. I expected the -m flag to be
present in sys.argv, but it most definitely isn't.

Is there any kind of workaround for this?

---

Reply to this email directly or view it on GitHub:
https://github.com/mitsuhiko/werkzeug/issues/461#issuecomment-119955695

Sent from my Android device with K-9 Mail. Please excuse my brevity.

I have a similar issue, where relative imports fail because the reloader executes the module as a non-package:

$ python -m myapp.entrypoints.website
 * Running on http://127.0.0.1:5000 (Press CTRL+C to quit)
 * Restarting with stat
Traceback (most recent call last):
  File "/tmp/myapp/entrypoints/website.py", line 9, in <module>
    from . import mymodule
ValueError: Attempted relative import in non-package

Using the comments from @untitaker, in Python < 3.3 we can detect if python -m was used (only then is __loader__ defined) and force the reloader to also use it by resetting sys.argv:

try:
    sys.argv = ['-m', __loader__.fullname] + sys.argv[1:]
except NameError:
    pass

But this is quite a hacky workaround (and only for Python < 3.3).

The current implementation in #531 doesn't fix this particular problem and unfortunately I don't see any way how it could.

I think I tried to fix this with loader once, but it showed vastly
different behavior from 2 to 3.

On Thu, Sep 10, 2015 at 01:26:56PM -0700, Martijn Vermaat wrote:

I have a similar issue, where relative imports fail because the reloader executes the module as a non-package:

$ python -m myapp.entrypoints.website
 * Running on http://127.0.0.1:5000 (Press CTRL+C to quit)
 * Restarting with stat
Traceback (most recent call last):
  File "/tmp/myapp/entrypoints/website.py", line 9, in <module>
    from . import mymodule
ValueError: Attempted relative import in non-package

Using the comments from @untitaker, in Python < 3.3 we can detect if python -m was used (only then is __loader__ defined) and force the reloader to also use it by resetting sys.argv:

try:
    sys.argv = ['-m', __loader__.fullname] + sys.argv[1:]
except NameError:
    pass

But this is quite a hacky workaround (and only for Python < 3.3).

---

Reply to this email directly or view it on GitHub:
https://github.com/mitsuhiko/werkzeug/issues/461#issuecomment-139369694

Sadly,

$ python -m werkzeug.serving weasyprint.navigator:app --reload --debug

• Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
• Restarting with stat
  Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/werkzeug/serving.py", line 45, in
  from ._compat import PY2
  ValueError: Attempted relative import in non-package

This bug of python can't be fixed propperly with python, so I suggest to provide a console-script

Any change in this? Just ran into this issue... (Python 3.6, no weasyprint, just python -m werkzeug.serving app:application)

I managed to get around the issue by doing something like:

PYTHONPATH=$PWD:$PYTHONPATH python -m myapp.entrypoints.website

_Edit: realized the solution was just above :arrow_up:_