Add support for manage.py shell -e 'run_some_code_as_django()'

[Håkan W]

I'm noticing a trend in my projects that I tend to create management commands that are just wrappers around a simple call that needs to be executed as Django.

Sometimes it would be so much easier to be able to just do this (from Fabric, or a bash script):

python manage.py shell -e 'do_something()'

[Collin Anderson]

I would personally use this pretty frequently.

[Adam Johnson]

Did you know? You can already do (at least in bash and zsh):

python manage.py shell <<< 'do_something()'

This sends the string in on stdin which shell simply interprets the same as typed commands. However it should be noted you can't do this in some shells or from e.g. subprocess.Popen without shell=True.

Also, if this does get implemented I'd suggest the -c flag to mirror python -c.

[Tim Graham]

I'm not convinced about accepting the ticket given the workaround Adam noted.

I think something like python -c "import django; django.setup(); ..." is also equivalent.

[Niels Van Och]

I started on a patch for this, I'll finish it up. In my head the feature has some merit.

[Tim Graham]

Adam's suggestion isn't completely equivalent as it will output the Python prompt too:

$ python manage.py shell <<< 'print(1)'
Python 3.5.0 (default, Sep 14 2015, 10:39:54) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> 1
>>> 

The discussion about deprecating the shell command in #19737 (ultimately closed as wontfix) also left me wondering if we should add more options to it.

I created a ​django-developers thread to get more feedback.

[Shai Berger]

Replying to timgraham:

Adam's suggestion isn't completely equivalent as it will output the Python prompt too:

$ python manage.py shell <<< 'print(1)'
Python 3.5.0 (default, Sep 14 2015, 10:39:54) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> 1
>>> 

More importantly, it "confiscates" stdin, so the called function cannot interact with the user:

$ python <<< 'print input()'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
EOFError: EOF when reading a line

[Adam Johnson]

Indeed it does confiscate. But interestingly python alone doesn't output the prompt:

$ python <<< 'print(23 * 7)'
161

So manage.py shell can maybe do something to avoid outputting the prompt in this case - which is still separate to the case of a flag of course.

[Simon Charette]

Replying to adamchainz:

Indeed it does confiscate. But interestingly python alone doesn't output the prompt:

$ python <<< 'print(23 * 7)'
161

So manage.py shell can maybe do something to avoid outputting the prompt in this case - which is still separate to the case of a flag of course.

In the long run it might just be easier to add this flag since we might have to also special case ipython and bpython also and from my understanding the <<< trick won't work on Windows.

[Hugo Osvaldo Barrera]

Why not just

import django
django.setup()

more_code_here

[Collin Anderson]

For me personally, I have a bunch of code in my ./manage.py that setups up the correct virtual environment so for me it takes a little more than django.setup().

[Tim Graham]

No strong opposition to the feature request has appeared so far.

[Tim Graham]

Left comments for improvement on the ​pull request.

[Niels Van Och]

Resolved the comments, except one, which I think can't be fixed.

[Tim Graham <timograham@…>]

In 7f7553dd:

Fixed #25680 -- Added django-admin shell --command option.

Add a -c option to the shell command to execute a command passed as a
string as Django.

[Mariusz Felisiak <felisiak.mariusz@…>]

In d26d1c1:

Refs #25680 -- Added shell tests for globals available in passed commands.