More docs, error messages, and tests

Doc/library/collections.rst

@@ -365,9 +365,13 @@ they add the ability to access fields by name instead of position index.
 
    The *fieldnames* are a single string with each fieldname separated by whitespace
    and/or commas (for example 'x y' or 'x, y').  Alternatively, the *fieldnames*
-   can be specified as a list of strings (such as ['x', 'y']).  Any valid
-   Python identifier may be used for a fieldname except for names starting and 
-   ending with double underscores.
+   can be specified as a list of strings (such as ['x', 'y']).
+
+   Any valid Python identifier may be used for a fieldname except for names
+   starting and ending with double underscores.  Valid identifiers consist of
+   letters, digits, and underscores but do not start with a digit and cannot be
+   a :mod:`keyword` such as *class*, *for*, *return*, *global*, *pass*, *print*,
+   or *raise*.
 
    If *verbose* is true, will print the class definition.
 

Lib/collections.py

@@ -2,6 +2,7 @@ __all__ = ['deque', 'defaultdict', 'named_tuple']
 
 from _collections import deque, defaultdict
 from operator import itemgetter as _itemgetter
+from keyword import iskeyword as _iskeyword
 import sys as _sys
 
 def named_tuple(typename, field_names, verbose=False):
@@ -35,6 +36,8 @@ def named_tuple(typename, field_names, verbose=False):
     for name in (typename,) + field_names:
         if not name.replace('_', '').isalnum():
             raise ValueError('Type names and field names can only contain alphanumeric characters and underscores: %r' % name)
+        if _iskeyword(name):
+            raise ValueError('Type names and field names cannot be a keyword: %r' % name)
         if name[0].isdigit():
             raise ValueError('Type names and field names cannot start with a number: %r' % name)
     seen_names = set()

Lib/test/test_collections.py

@@ -11,11 +11,17 @@ class TestNamedTuple(unittest.TestCase):
         self.assertEqual(Point.__slots__, ())
         self.assertEqual(Point.__module__, __name__)
         self.assertEqual(Point.__getitem__, tuple.__getitem__)
-        self.assertRaises(ValueError, named_tuple, 'abc%', 'def ghi')
-        self.assertRaises(ValueError, named_tuple, 'abc', 'def g%hi')
-        self.assertRaises(ValueError, named_tuple, 'abc', '__def__ ghi')
-        self.assertRaises(ValueError, named_tuple, 'abc', 'def def ghi')
-        self.assertRaises(ValueError, named_tuple, 'abc', '8def 9ghi')
+
+        self.assertRaises(ValueError, named_tuple, 'abc%', 'efg ghi')       # type has non-alpha char
+        self.assertRaises(ValueError, named_tuple, 'class', 'efg ghi')      # type has keyword
+        self.assertRaises(ValueError, named_tuple, '9abc', 'efg ghi')       # type starts with digit
+
+        self.assertRaises(ValueError, named_tuple, 'abc', 'efg g%hi')       # field with non-alpha char
+        self.assertRaises(ValueError, named_tuple, 'abc', 'abc class')      # field has keyword
+        self.assertRaises(ValueError, named_tuple, 'abc', '8efg 9ghi')      # field starts with digit
+        self.assertRaises(ValueError, named_tuple, 'abc', '__efg__ ghi')    # field with double underscores
+        self.assertRaises(ValueError, named_tuple, 'abc', 'efg efg ghi')    # duplicate field
+
         named_tuple('Point0', 'x1 y2')   # Verify that numbers are allowed in names
 
     def test_instance(self):
@@ -66,7 +72,6 @@ class TestNamedTuple(unittest.TestCase):
         self.assertEqual(p.y, y)
         self.assertRaises(AttributeError, eval, 'p.z', locals())
 
-
     def test_odd_sizes(self):
         Zero = named_tuple('Zero', '')
         self.assertEqual(Zero(), ())