shell_plus

synopsis:Django shell with autoloading of the apps database models

Interactive Python Shells

There is support for three different types of interactive python shells.

IPython:

$ ./manage.py shell_plus --ipython

bpython:

$ ./manage.py shell_plus --bpython

ptpython:

$ ./manage.py shell_plus --ptpython

Python:

$ ./manage.py shell_plus --plain

The default resolution order is: ptpython, bpython, ipython, python.

You can also set the configuration option SHELL_PLUS to explicitly specify which version you want.

# Always use IPython for shell_plus
SHELL_PLUS = "ipython"

It is also possible to use IPython Notebook, an interactive Python shell which uses a web browser as its user interface, as an alternative shell:

$ ./manage.py shell_plus --notebook

In addition to being savable, IPython Notebooks can be updated (while running) to reflect changes in a Django application’s code with the menu command Kernel > Restart.

Configuration

Sometimes, models from your own apps and other people’s apps have colliding names, or you may want to completely skip loading an app’s models. Here are some examples of how to do that.

Note: These settings are only used inside shell_plus and will not affect your environment.

# Rename the automatic loaded module Messages in the app blog to blog_messages.
SHELL_PLUS_MODEL_ALIASES = {'blog': {'Messages': 'blog_messages'},}
# Prefix all automatically loaded models in the app blog with myblog.
SHELL_PLUS_APP_PREFIXES = {'blog': 'myblog',}
# Dont load the 'sites' app, and skip the model 'pictures' in the app 'blog'
SHELL_PLUS_DONT_LOAD = ['sites', 'blog.pictures']
# Dont load any models
SHELL_PLUS_DONT_LOAD = ['*']

You can also combine model_aliases and dont_load. When referencing nested modules, e.g. somepackage.someapp.models.somemodel, omit the package name and the reference to models. For example:

SHELL_PLUS_DONT_LOAD = ['someapp.somemodel', ]  # This works
SHELL_PLUS_DONT_LOAD = ['somepackage.someapp.models.somemodel', ]  # This does NOT work

It is possible to ignore autoloaded modules when using manage.py, like:

$ ./manage.py shell_plus --dont-load app1 --dont-load app2.module1

Command line parameters and settings in the configuration file are merged, so you can safely append modules to ignore from the commandline for one-time usage.

Collision resolvers

You don’t have to worry about inaccessibility of models with conflicting names.

If you have conflicting model names, all conflicts can be resolved automatically. All models will be available under shell_plus, some of them with intuitive aliases.

This mechanism is highly configurable and you must only set SHELL_PLUS_MODEL_IMPORTS_RESOLVER. You should set full path to collision resolver class.

All predefined collision resolvers are in django_extensions.collision_resolvers module. Example:

SHELL_PLUS_MODEL_IMPORTS_RESOLVER = 'django_extensions.collision_resolvers.FullPathCR'

All collision resolvers searches for models with the same name.

If conflict is detected they decides, which model to choose. Some of them are creating aliases for all conflicting models.

Example

Suppose that we have two apps:

  • programming(with models Language and Framework)
  • workers(with models Language and Worker)

‘workers’ app is last in alphabetical order, but suppose that ‘programming’ app is occurs firstly in INSTALLED_APPS.

Collision resolvers won’t change aliases for models Framework and Worker, because their names are unique. There are several types of collision resolvers:

LegacyCR

Default collision resolver. Model from last application in alphabetical order is selected:

from workers import Language

InstalledAppsOrderCR

Collision resolver which selects first model from INSTALLED_APPS. You can set your own app priorities list subclassing him and overwriting APP_PRIORITIES field.

This collision resolver will select model from first app on this list. If both app’s are absent on this list, resolver will choose model from first app in alphabetical order:

from programming import Language

FullPathCR

Collision resolver which transform full model name to alias by changing dots to underscores. He also removes ‘models’ part of alias, because all models are in models.py files.

Model from last application in alphabetical order is selected:

from programming import Language (as programming_Language)
from workers import Language, Language (as workers_Language)

AppNamePrefixCR

Collision resolver which transform pair (app name, model_name) to alias {app_name}_{model_name}. Model from last application in alphabetical order is selected.

Result is different than FullPathCR, when model has app_label other than current app:

from programming import Language (as programming_Language)
from workers import Language, Language (as workers_Language)

AppNameSuffixCR

Collision resolver which transform pair (app name, model_name) to alias {model_name}_{app_name}

Model from last application in alphabetical order is selected:

from programming import Language (as Language_programming)
from workers import Language, Language (as Language_workers)

AppNamePrefixCustomOrderCR

Collision resolver which is mixin of AppNamePrefixCR and InstalledAppsOrderCR.

In case of collisions he sets aliases like AppNamePrefixCR, but sets default model using InstalledAppsOrderCR:

from programming import Language, Language (as programming_Language)
from workers import Language (as workers_Language)

AppNameSuffixCustomOrderCR

Collision resolver which is mixin of AppNameSuffixCR and InstalledAppsOrderCR.

In case of collisions he sets aliases like AppNameSuffixCR, but sets default model using InstalledAppsOrderCR:

from programming import Language, Language (as Language_programming)
from workers import Language (as Language_workers)

FullPathCustomOrderCR

Collision resolver which is mixin of FullPathCR and InstalledAppsOrderCR.

In case of collisions he sets aliases like FullPathCR, but sets default model using InstalledAppsOrderCR:

from programming import Language, Language (as programming_Language)
from workers import Language (as workers_Language)

Writing your custom collision resolver

You can customize models import behaviour by subclassing one of the abstract collision resolvers:

PathBasedCR

Abstract resolver which transforms full model name into alias. To use him you need to overwrite transform_import function which should have one parameter.

It will be full model name. It should return valid alias as str instance.

AppNameCR

Abstract collision resolver which transform pair (app name, model_name) to alias by changing dots to underscores.

You must define MODIFICATION_STRING which should be string to format with two keyword arguments: app_name and model_name. For example: {app_name}_{model_name}.

Model from last application in alphabetical order is selected.

You can mix PathBasedCR or AppNameCR with InstalledAppsOrderCR, but InstalledAppsOrderCR should be second base class.

BaseCR

Abstract base collision resolver. All collision resolvers needs to inherit from this class.

To write custom collision resolver you need to overwrite resolve_collisions function. It receives Dict[str, List[str]] where key is model name and values are full model names (full model name means: module + model_name).

You should return Dict[str, str], where key is model name and value is full model name.

IPython Notebook

There are two settings that you can use to pass your custom options to the IPython Notebook in your Django settings.

The first one is NOTEBOOK_ARGUMENTS that can be used to hold those options that available via:

$ ipython notebook -h

For example:

NOTEBOOK_ARGUMENTS = [
    '--ip', 'x.x.x.x',
    '--port', 'xx',
]

Another one is IPYTHON_ARGUMENTS that for those options that available via:

$ ipython -h

The Django settings module and database models are auto-loaded into the interactive shell’s global namespace also for IPython Notebook.

Auto-loading is done by a custom IPython extension which is activated by default by passing the --ext django_extensions.management.notebook_extension argument to the Notebook. If you need to pass custom options to the IPython Notebook, you can override the default options in your Django settings using the IPYTHON_ARGUMENTS setting. For example:

IPYTHON_ARGUMENTS = [
    '--ext', 'django_extensions.management.notebook_extension',
    '--ext', 'myproject.notebook_extension',
    '--debug',
]

To activate auto-loading, remember to either include the django-extensions’ default notebook extension or copy its auto-loading code into your own extension.

Note that the IPython Notebook feature doesn’t currently honor the --dont-load option.

Additional Imports

In addition to importing the models you can specify other items to import by default. These are specified in SHELL_PLUS_PRE_IMPORTS and SHELL_PLUS_POST_IMPORTS. The former is imported before any other imports (such as the default models import) and the latter is imported after any other imports. Both have similar syntax. So in your settings.py file:

SHELL_PLUS_PRE_IMPORTS = [
    ('module.submodule1', ('class1', 'function2')),
    ('module.submodule2', 'function3'),
    ('module.submodule3', '*'),
    'module.submodule4'
]

The above example would directly translate to the following python code which would be executed before the automatic imports:

from module.submodule1 import class1, function2
from module.submodule2 import function3
from module.submodule3 import *
import module.submodule4

These symbols will be available as soon as the shell starts.

Database application signature

If using PostgreSQL the application_name is set by default to django_shell to help identify queries made under shell_plus.

SQL queries

If the configuration option DEBUG is set to True, it is possible to print SQL queries as they’re executed in shell_plus like:

$ ./manage.py shell_plus --print-sql

You can also set the configuration option SHELL_PLUS_PRINT_SQL to omit the above command line option.

# print SQL queries in shell_plus
SHELL_PLUS_PRINT_SQL = True