python django shell (ipython) unexpected behavior

Django shell behaves (at least for me) unexpected when working with locale settings. Form validation of a comma separated decimal field works when calling from external script and fails on calling from django shell (ipython).

Starting a new Project I got the following files:

local_forms/
├── local_forms
│   ├── __init__.py
│   ├── models.py
│   ├── settings.py
│   ├── urls.py
│   └── wsgi.py
├── manage.py
├── my_form.py
├── test_form.py

local_forms/models.py:

from django.db import models

class MyModel(models.Model):
    val=models.DecimalField("value",max_digits=11,decimal_places=2)

my_form.py

from django import forms
from django.conf import settings
from local_forms.models import MyModel


class MyForm(forms.ModelForm):
    val = forms.DecimalField(localize=True)

    def __init__(self,*args,**kwargs):
        super(MyForm,self).__init__(*args,**kwargs)
        self.fields['val'].localize=True
        if __debug__:
            print self.fields['val'].localize
            print ("Separator: "+settings.DECIMAL_SEPARATOR)
            print ("Language: " +settings.LANGUAGE_CODE)

    class Meta:
        model=MyModel

test_form.py:

#!/usr/bin/env python
import os
import sys

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "local_forms.settings")

    import my_form

    form=my_form.MyForm({'val':'0,2'})

    print ("Is bound: %s" % form.is_bound)
    print ("Form valid %s" % form.is_valid())
    print("Errors in val: %s" % form['val'].errors)

Calling ./test_form.py yields:

./test_form.py

True
Separator: .
Language: de-de
Is bound: True
Form valid True
Errors in val:

Doing the same thing in django shell: python manage.py shell

In [1]: import my_form as mf

In [2]: form=mf.MyForm({'val':'0,2'})
True
Separator: .
Language: de-de

In [3]: form.is_valid()
Out[3]: False

In [4]: form['val'].errors
Out[4]: [u'Enter a number.']

To sum up: If i start the django shell (which on my pc uses ipython) the locale somehow does not work. Doing exactly the same in a script works perfectly. Can you please explain this behavior?

The Django management commands, including shell, reset the language to 'en-us', hence your issue. The explanation of this behaviour is in the Django Documentation:

By default, the BaseCommand.execute() method sets the hardcoded ‘en-us’ locale because some commands shipped with Django perform several tasks (for example, user-facing content rendering and database population) that require a system-neutral string language (for which we use ‘en-us’).

Your example does work in the shell if you activate the proper language:

>>> from django.utils.translation import get_language
>>> get_language()
  > 'en-us'
>>> import my_form as mf
>>> form=mf.MyForm({'val':'0,2'})
True
Separator: .
Language: de-de
>>> form.is_valid()
  > False
>>> from django.utils.translation import activate
>>> activate('de-de')
>>> get_language()
  > 'de-de'
>>> form=mf.MyForm({'val':'0,2'})
True
Separator: .
Language: de-de
>>> form.is_valid()
  > True

On a side note, you should always check the current language using get_locale() instead of relying on settings.