Use
Sample.objects.filter(date__range=["2011-01-01", "2011-01-31"])
Or if you are just trying to filter month wise:
Sample.objects.filter(date__year='2011',
date__month='01')
Edit
As Bernhard Vallant said, if you want a queryset which excludes the specified range ends
you should consider his solution, which utilizes gt/lt (greater-than/less-than).
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