mirror of https://github.com/python/cpython
Minor fix-ups to named tuples:
* Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator.
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@ -388,6 +388,8 @@ Example::
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__slots__ = ()
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_fields = ('x', 'y')
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def __new__(cls, x, y):
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return tuple.__new__(cls, (x, y))
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@ -402,11 +404,7 @@ Example::
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def _replace(self, **kwds):
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'Return a new Point object replacing specified fields with new values'
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return Point._cast(map(kwds.get, ('x', 'y'), self))
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@property
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def _fields(self):
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return ('x', 'y')
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return self.__class__._cast(map(kwds.get, ('x', 'y'), self))
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x = property(itemgetter(0))
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y = property(itemgetter(1))
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@ -439,17 +437,22 @@ by the :mod:`csv` or :mod:`sqlite3` modules::
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print emp.name, emp.title
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In addition to the methods inherited from tuples, named tuples support
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three additonal methods and a read-only attribute.
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three additonal methods and one attribute.
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.. method:: namedtuple._cast(iterable)
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Class method returning a new instance taking the positional arguments from the *iterable*.
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Useful for casting existing sequences and iterables to named tuples:
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Class method returning a new instance taking the positional arguments from the
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*iterable*. Useful for casting existing sequences and iterables to named tuples.
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This fast constructor does not check the length of the inputs. To achieve the
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same effect with length checking, use the star-operator instead.
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::
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>>> t = [11, 22]
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>>> Point._cast(t)
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>>> Point._cast(t) # fast conversion
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Point(x=11, y=22)
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>>> Point(*t) # slow conversion with length checking
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Point(x=11, y=22)
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.. method:: somenamedtuple._asdict()
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@ -476,7 +479,7 @@ three additonal methods and a read-only attribute.
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.. attribute:: somenamedtuple._fields
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Return a tuple of strings listing the field names. This is useful for introspection
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Tuple of strings listing the field names. This is useful for introspection
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and for creating new named tuple types from existing named tuples.
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::
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@ -60,6 +60,7 @@ def namedtuple(typename, field_names, verbose=False):
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template = '''class %(typename)s(tuple):
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'%(typename)s(%(argtxt)s)' \n
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__slots__ = () \n
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_fields = %(field_names)r \n
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def __new__(cls, %(argtxt)s):
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return tuple.__new__(cls, (%(argtxt)s)) \n
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_cast = classmethod(tuple.__new__) \n
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@ -70,10 +71,7 @@ def namedtuple(typename, field_names, verbose=False):
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return {%(dicttxt)s} \n
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def _replace(self, **kwds):
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'Return a new %(typename)s object replacing specified fields with new values'
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return %(typename)s._cast(map(kwds.get, %(field_names)r, self)) \n
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@property
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def _fields(self):
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return %(field_names)r \n\n''' % locals()
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return self.__class__._cast(map(kwds.get, %(field_names)r, self)) \n\n''' % locals()
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for i, name in enumerate(field_names):
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template += ' %s = property(itemgetter(%d))\n' % (name, i)
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if verbose:
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@ -17,6 +17,7 @@ class TestNamedTuple(unittest.TestCase):
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self.assertEqual(Point.__slots__, ())
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self.assertEqual(Point.__module__, __name__)
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self.assertEqual(Point.__getitem__, tuple.__getitem__)
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self.assertEqual(Point._fields, ('x', 'y'))
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self.assertRaises(ValueError, namedtuple, 'abc%', 'efg ghi') # type has non-alpha char
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self.assertRaises(ValueError, namedtuple, 'class', 'efg ghi') # type has keyword
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@ -51,14 +52,6 @@ class TestNamedTuple(unittest.TestCase):
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self.assertEqual(p._replace(x=1), (1, 22)) # test _replace method
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self.assertEqual(p._asdict(), dict(x=11, y=22)) # test _asdict method
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# Verify that _fields is read-only
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try:
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p._fields = ('F1' ,'F2')
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except AttributeError:
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pass
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else:
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self.fail('The _fields attribute needs to be read-only')
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# verify that field string can have commas
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Point = namedtuple('Point', 'x, y')
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p = Point(x=11, y=22)
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