Skip to main content
Join the official Python Developers Survey 2018 and win valuable prizes: Start the survey!

Django friendly finite state machine support.

Project description

Django friendly finite state machine support

django-fsm adds declarative states management for django models.
Instead of adding some state field to a django model, and manage it
values by hand, you could use FSMState field and mark model methods
with the `transition` decorator. Your method will contain the side-effects
of the state change.

The decorator also takes a list of conditions, all of which must be met
before a transition is allowed.


$ pip install django-fsm

Or, for the latest git version

$ pip install -e git://

Library has full Python 3 support, for the graph transition drawing
you should install python3 compatible graphviz version
from git+


Add FSMState field to your model

from django_fsm import FSMField, transition

class BlogPost(models.Model):
state = FSMField(default='new')

Use the `transition` decorator to annotate model methods

@transition(field=state, source='new', target='published')
def publish(self):
This function may contain side-effects,
like updating caches, notifying users, etc.
The return value will be discarded.

`source` parameter accepts a list of states, or an individual state.
You can use `*` for source, to allow switching to `target` from any state.

If calling publish() succeeds without raising an exception, the state field
will be changed, but not written to the database.

from django_fsm import can_proceed

def publish_view(request, post_id):
post = get_object__or_404(BlogPost, pk=post_id)
if not can_proceed(post.publish):
raise Http404;

return redirect('/')

If some conditions are required to be met before the changing state, use the
`conditions` argument to `transition`. `conditions` must be a list of functions
that takes one argument, the model instance. The function must return either
`True` or `False` or a value that evaluates to `True` or `False`. If all
functions return `True`, all conditions are considered to be met and transition
is allowed to happen. If one of the functions return `False`, the transition
will not happen. These functions should not have any side effects.

You can use ordinary functions

def can_publish(instance):
# No publishing after 17 hours
if > 17:
return False
return True

Or model methods

def can_destroy(self):
return self.is_under_investigation()

Use the conditions like this:

@transition(field=state, source='new', target='published', conditions=[can_publish])
def publish(self):
Side effects galore

@transition(field=state, source='*', target='destroyed', conditions=[can_destroy])
def destroy(self):
Side effects galore

You could instantiate field with protected=True option, that prevents direct state field modification

class BlogPost(models.Model):
state = FSMField(default='new', protected=True)

model = BlogPost()
model.state = 'invalid' # Raises AttributeError

### get_available_FIELD_transitions
Returns all transitions data available in current state

### get_all_FIELD_transitions
Enumerates all declared transitions

### Foreign Key constraints support

If you store the states in the db table you could use FSMKeyField to
ensure Foreign Key database integrity.

In your model :

class DbState(models.Model):
id = models.CharField(primary_key=True, max_length=50)
label = models.CharField(max_length=255)

def __unicode__(self);
return self.label

class BlogPost(models.Model):
state = FSMKeyField(DbState, default='new')

@transition(field=state, source='new', target='published')
def publish(self):

In your fixtures/initial_data.json :

"pk": "new",
"model": "myapp.dbstate",
"fields": {
"label": "_NEW_"
"pk": "published",
"model": "myapp.dbstate",
"fields": {
"label": "_PUBLISHED_"
}, ...

Note : source and target parameters in @transition decorator use pk values of DBState model
as names, even if field "real" name is used, without _id postfix, as field parameter.

### Integer Field support

You can also use `FSMIntegerField`. This is handy when you want to use enum style constants. This field is also `db_index=True` by default for speedy db loookups.

class BlogPostStateEnum(object):
NEW = 10

class BlogPostWithIntegerField(models.Model):
state = FSMIntegerField(default=BlogPostStateEnum.NEW)

@transition(source=BlogPostStateEnum.NEW, target=BlogPostStateEnum.PUBLISHED)
def publish(self):

### Signals

`django_fsm.signals.pre_transition` and `django_fsm.signals.post_transition` are called before
and after allowed transition. No signals on invalid transition are called.

Arguments sent with these signals:

The model class.

The actual instance being procceed

Transition name

Source model state

Target model state

### Drawing transitions

Renders a graphical overview of your models states transitions

# Create a dot file
$ ./ graph_transitions >

# Create a PNG image file only for specific model
$ ./ graph_transitions -o blog_transitions.png myapp.Blog


<img src="" alt="django-fsm" width="100px"/>

### django-fsm 2.0.0 2014-03-15
* Backward incompatible release
* All public code import moved directly to django_fsm package
* Correct support for several @transitions decorator with different source states and conditions on same method
* save parameter from transition decorator removed
* get_available_FIELD_transitions return Transition data object instead of tuple
* Models got get_available_FIELD_transitions, even if field specified as string reference
* New get_all_FIELD_transitions method contributed to class

### django-fsm 1.6.0 2014-03-15
* FSMIntegerField and FSMKeyField support

### django-fsm 1.5.1 2014-01-04

* Ad-hoc support for state fields from proxy and inherited models

### django-fsm 1.5.0 2013-09-17

* Python 3 compatibility

### django-fsm 1.4.0 2011-12-21

* Add graph_transition command for drawing state transition picture

### django-fsm 1.3.0 2011-07-28

* Add direct field modification protection

### django-fsm 1.2.0 2011-03-23

* Add pre_transition and post_transition signals

### django-fsm 1.1.0 2011-02-22

* Add support for transition conditions
* Allow multiple FSMField in one model
* Contribute get_available_FIELD_transitions for model class

### django-fsm 1.0.0 2010-10-12

* Initial public release

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
django-fsm-2.0.1.tar.gz (5.0 kB) Copy SHA256 hash SHA256 Source None Mar 24, 2014

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page