Sync-up named tuples with the latest version of the ASPN recipe.
Allows optional commas in the field-name spec (help when named tuples are used in conjuction with sql queries).
Adds the __fields__ attribute for introspection and to support conversion to dictionary form.
Adds a __replace__() method similar to str.replace() but using a named field as a target.
Clean-up spelling and presentation in doc-strings.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 28d48bf..7b639b3 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -374,8 +374,8 @@
.. versionadded:: 2.6
- The *fieldnames* are specified in a single string and are separated by spaces.
- Any valid Python identifier may be used for a field name.
+ The *fieldnames* are specified in a single string and are separated by spaces
+ and/or commas. Any valid Python identifier may be used for a field name.
Example::
@@ -395,7 +395,7 @@
The use cases are the same as those for tuples. The named factories assign
meaning to each tuple position and allow for more readable, self-documenting
- code. Named tuples can also be used to assign field names to tuples returned
+ code. Named tuples can also be used to assign field names to tuples returned
by the :mod:`csv` or :mod:`sqlite3` modules. For example::
from itertools import starmap
@@ -412,6 +412,38 @@
>>> print Color(*m.popitem())
Color(name='blue', code=3)
+In addition to the methods inherited from tuples, named tuples support
+an additonal method and an informational read-only attribute.
+
+.. method:: somenamedtuple.replace(field, value)
+
+ Return a new instance of the named tuple with *field* replaced with *value*.
+
+ Examples::
+
+ >>> p = Point(x=11, y=22)
+ >>> p.__replace__('x', 33)
+ Point(x=33, y=22)
+
+ >>> for recordnum, record in inventory:
+ ... inventory[recordnum] = record.replace('total', record.price * record.quantity)
+
+
+.. attribute:: somenamedtuple.__fields__
+
+ Return a tuple of strings listing the field names. This is useful for introspection,
+ for converting a named tuple instance to a dictionary, and for creating new named tuple
+ types from existing types.
+
+ Examples::
+
+ >>> dict(zip(p.__fields__, p)) # make a dictionary from a named tuple instance
+ {'y': 20, 'x': 10}
+
+ >>> ColorPoint = NamedTuple('ColorPoint', ' '.join(Point.__fields__) + ' color')
+ >>> ColorPoint(10, 20, 'red')
+ ColorPoint(x=10, y=20, color='red')
+
.. rubric:: Footnotes
.. [#] For information on the star-operator see
diff --git a/Lib/collections.py b/Lib/collections.py
index 4a860dd..c2b1176 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -8,33 +8,42 @@
"""Returns a new subclass of tuple with named fields.
>>> Point = NamedTuple('Point', 'x y')
- >>> Point.__doc__ # docstring for the new class
+ >>> Point.__doc__ # docstring for the new class
'Point(x, y)'
- >>> p = Point(11, y=22) # instantiate with positional args or keywords
- >>> p[0] + p[1] # works just like the tuple (11, 22)
+ >>> p = Point(11, y=22) # instantiate with positional args or keywords
+ >>> p[0] + p[1] # works just like the tuple (11, 22)
33
- >>> x, y = p # unpacks just like a tuple
+ >>> x, y = p # unpacks just like a tuple
>>> x, y
(11, 22)
- >>> p.x + p.y # fields also accessable by name
+ >>> p.x + p.y # fields also accessable by name
33
- >>> p # readable __repr__ with name=value style
+ >>> p # readable __repr__ with name=value style
Point(x=11, y=22)
+ >>> p.__replace__('x', 100) # __replace__() is like str.replace() but targets a named field
+ Point(x=100, y=22)
+ >>> d = dict(zip(p.__fields__, p)) # use __fields__ to make a dictionary
+ >>> d['x']
+ 11
"""
- field_names = s.split()
- if not ''.join([typename] + field_names).replace('_', '').isalnum():
+ field_names = tuple(s.replace(',', ' ').split()) # names separated by spaces and/or commas
+ if not ''.join((typename,) + field_names).replace('_', '').isalnum():
raise ValueError('Type names and field names can only contain alphanumeric characters and underscores')
argtxt = ', '.join(field_names)
reprtxt = ', '.join('%s=%%r' % name for name in field_names)
template = '''class %(typename)s(tuple):
'%(typename)s(%(argtxt)s)'
__slots__ = ()
+ __fields__ = %(field_names)r
def __new__(cls, %(argtxt)s):
return tuple.__new__(cls, (%(argtxt)s,))
def __repr__(self):
return '%(typename)s(%(reprtxt)s)' %% self
+ def __replace__(self, field, value):
+ 'Return a new %(typename)s object replacing one field with a new value'
+ return %(typename)s(**dict(zip(%(field_names)r, self) + [(field, value)]))
''' % locals()
for i, name in enumerate(field_names):
template += '\n %s = property(itemgetter(%d))\n' % (name, i)
@@ -51,9 +60,9 @@
if __name__ == '__main__':
- # verify that instances are pickable
+ # verify that instances can be pickled
from cPickle import loads, dumps
- Point = NamedTuple('Point', 'x y')
+ Point = NamedTuple('Point', 'x, y')
p = Point(x=10, y=20)
assert p == loads(dumps(p))
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index f5dad7d..94015b4 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -30,6 +30,13 @@
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.__fields__, ('x', 'y')) # test __fields__ attribute
+ self.assertEqual(p.__replace__('x', 1), (1, 22)) # test __replace__ method
+
+ # verify that field string can have commas
+ Point = NamedTuple('Point', 'x, y')
+ p = Point(x=11, y=22)
+ self.assertEqual(repr(p), 'Point(x=11, y=22)')
def test_tupleness(self):
Point = NamedTuple('Point', 'x y')