A defaultnamedtuple which creates a namedtuple with default values when none are given.

collection.py

""" Additional collections to augment Python's collections module.
"""

from collections import namedtuple

def defaultnamedtuple(
    typename,
    field_names,
    verbose=False,
    rename=False,
    default_factory=None
  ):
  """A factory for namedtuples with default values similar to defaultdict.

  The default_factory is a callable which returns default values.  All
  other functionality matches namedtuple.  When default_factory is None, the
  default, the defaultnamedtuple acts exactly the same as a namedtuple.

  """

  tuple_class = namedtuple(typename, field_names, verbose, rename)

  class sub_tuple_class(tuple_class):
    def __new__(self, *args, **kwargs):

      if default_factory:
        missing_args = field_names[len(args):]
        for missing_arg in missing_args:
          if not missing_arg in kwargs:
            kwargs[missing_arg] = default_factory()

      return super(sub_tuple_class, self).__new__(self, *args, **kwargs)

  return sub_tuple_class

if __name__ == '__main__':

  import unittest

  class defaultnamedtupleTestCase(unittest.TestCase):
    """ A test case for defaultnamedtuple class factory"""

    def setUp(self):
      """Initial setup for all tests"""

      self.class_str = 'Test(x=0, y=0, z=0)'
      self.class_name = 'Test'
      self.field_names = ['x', 'y', 'z']
      self.default_value = 0
      self.test_default = defaultnamedtuple(
        self.class_name,
        self.field_names,
        default_factory=lambda:self.default_value
      )
      self.test_no_default = defaultnamedtuple(
        self.class_name,
        self.field_names
      )
      self.reference = namedtuple(self.class_name, self.field_names)

    def testNoArgsOrKwargs(self):
      """Test defaultnamedtuple with no args or kwargs"""
      a = self.test_default()
      b = self.reference(
        self.default_value,
        self.default_value,
        self.default_value
      )

      self.assertEqual(a, b)

    def testSomeArgs(self):
      """Test defaultnamedtuple with some but not all args given."""
      a = self.test_default(1, 1)
      b = self.reference(
        1,
        1,
        self.default_value
      )

      self.assertEqual(a, b)

    def testSomeKwargs(self):
      """Test defaultnamedtuple with some but not all kwargs given."""

      a = self.test_default(x=1, z=1)
      b = self.reference(
        x=1,
        y=self.default_value,
        z=1
      )

      self.assertEqual(a, b)

  unittest.main()