'Explicitly checks for the string \'True\' and \'False\', which is what a
hidden field will submit for True and False, and for \'1\' and \'0\', which
is what a RadioField will submit. Unlike the Booleanfield we need to
explicitly check for True, because we are not using the bool() function'

def to_python(self, value):

    if (value in (True, u'True', u'1')):
        return True
    elif (value in (False, u'False', u'0')):
        return False
    else:
        return None
