Improve namedtuple's _cast() method with a docstring, new name, and error-checking.
diff --git a/Lib/collections.py b/Lib/collections.py
index 487b119..2a58b86 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -54,6 +54,7 @@
seen_names.add(name)
# Create and fill-in the class template
+ numfields = len(field_names)
argtxt = repr(field_names).replace("'", "")[1:-1] # tuple repr without parens or quotes
reprtxt = ', '.join('%s=%%r' % name for name in field_names)
dicttxt = ', '.join('%r: t[%d]' % (name, pos) for pos, name in enumerate(field_names))
@@ -63,7 +64,13 @@
_fields = %(field_names)r \n
def __new__(cls, %(argtxt)s):
return tuple.__new__(cls, (%(argtxt)s)) \n
- _cast = classmethod(tuple.__new__) \n
+ @classmethod
+ def _make(cls, iterable):
+ 'Make a new %(typename)s object from a sequence or iterable'
+ result = tuple.__new__(cls, iterable)
+ if len(result) != %(numfields)d:
+ raise TypeError('Expected %(numfields)d arguments, got %%d' %% len(result))
+ return result \n
def __repr__(self):
return '%(typename)s(%(reprtxt)s)' %% self \n
def _asdict(t):
@@ -71,7 +78,7 @@
return {%(dicttxt)s} \n
def _replace(self, **kwds):
'Return a new %(typename)s object replacing specified fields with new values'
- return self.__class__._cast(map(kwds.get, %(field_names)r, self)) \n\n''' % locals()
+ return self.__class__._make(map(kwds.get, %(field_names)r, self)) \n\n''' % locals()
for i, name in enumerate(field_names):
template += ' %s = property(itemgetter(%d))\n' % (name, i)
if verbose:
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 5e71399..c17b76d 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -32,6 +32,9 @@
namedtuple('Point0', 'x1 y2') # Verify that numbers are allowed in names
namedtuple('_', 'a b c') # Test leading underscores in a typename
+ self.assertRaises(TypeError, Point._make, [11]) # catch too few args
+ self.assertRaises(TypeError, Point._make, [11, 22, 33]) # catch too many args
+
def test_instance(self):
Point = namedtuple('Point', 'x y')
p = Point(11, 22)
@@ -47,7 +50,7 @@
self.assertEqual(repr(p), 'Point(x=11, y=22)')
self.assert_('__dict__' not in dir(p)) # verify instance has no dict
self.assert_('__weakref__' not in dir(p))
- self.assertEqual(p, Point._cast([11, 22])) # test _cast classmethod
+ self.assertEqual(p, Point._make([11, 22])) # test _make classmethod
self.assertEqual(p._fields, ('x', 'y')) # test _fields attribute
self.assertEqual(p._replace(x=1), (1, 22)) # test _replace method
self.assertEqual(p._asdict(), dict(x=11, y=22)) # test _asdict method
@@ -84,14 +87,14 @@
def test_odd_sizes(self):
Zero = namedtuple('Zero', '')
self.assertEqual(Zero(), ())
- self.assertEqual(Zero._cast([]), ())
+ self.assertEqual(Zero._make([]), ())
self.assertEqual(repr(Zero()), 'Zero()')
self.assertEqual(Zero()._asdict(), {})
self.assertEqual(Zero()._fields, ())
Dot = namedtuple('Dot', 'd')
self.assertEqual(Dot(1), (1,))
- self.assertEqual(Dot._cast([1]), (1,))
+ self.assertEqual(Dot._make([1]), (1,))
self.assertEqual(Dot(1).d, 1)
self.assertEqual(repr(Dot(1)), 'Dot(d=1)')
self.assertEqual(Dot(1)._asdict(), {'d':1})
@@ -104,7 +107,7 @@
Big = namedtuple('Big', names)
b = Big(*range(n))
self.assertEqual(b, tuple(range(n)))
- self.assertEqual(Big._cast(range(n)), tuple(range(n)))
+ self.assertEqual(Big._make(range(n)), tuple(range(n)))
for pos, name in enumerate(names):
self.assertEqual(getattr(b, name), pos)
repr(b) # make sure repr() doesn't blow-up