Users demand iterable input for named tuples. The author capitulates.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 5fcb293..9e8f3e3 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -391,6 +391,8 @@
def __new__(cls, x, y):
return tuple.__new__(cls, (x, y))
+ _cast = classmethod(tuple.__new__)
+
def __repr__(self):
return 'Point(x=%r, y=%r)' % self
@@ -400,7 +402,7 @@
def _replace(self, **kwds):
'Return a new Point object replacing specified fields with new values'
- return Point(*map(kwds.get, ('x', 'y'), self))
+ return Point._cast(map(kwds.get, ('x', 'y'), self))
@property
def _fields(self):
@@ -425,34 +427,31 @@
EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')
- from itertools import starmap
import csv
- for emp in starmap(EmployeeRecord, csv.reader(open("employees.csv", "rb"))):
+ for emp in map(EmployeeRecord._cast, csv.reader(open("employees.csv", "rb"))):
print emp.name, emp.title
import sqlite3
conn = sqlite3.connect('/companydata')
cursor = conn.cursor()
cursor.execute('SELECT name, age, title, department, paygrade FROM employees')
- for emp in starmap(EmployeeRecord, cursor.fetchall()):
+ for emp in map(EmployeeRecord._cast, cursor.fetchall()):
print emp.name, emp.title
-When casting a single record to a named tuple, use the star-operator [#]_ to unpack
-the values::
+In addition to the methods inherited from tuples, named tuples support
+three additonal methods and a read-only attribute.
+
+.. method:: namedtuple._cast(iterable)
+
+ Class method returning a new instance taking the positional arguments from the *iterable*.
+ Useful for casting existing sequences and iterables to named tuples:
+
+::
>>> t = [11, 22]
- >>> Point(*t) # the star-operator unpacks any iterable object
+ >>> Point._cast(t)
Point(x=11, y=22)
-When casting a dictionary to a named tuple, use the double-star-operator::
-
- >>> d = {'x': 11, 'y': 22}
- >>> Point(**d)
- Point(x=11, y=22)
-
-In addition to the methods inherited from tuples, named tuples support
-two additonal methods and a read-only attribute.
-
.. method:: somenamedtuple._asdict()
Return a new dict which maps field names to their corresponding values:
@@ -498,6 +497,12 @@
>>> getattr(p, 'x')
11
+When casting a dictionary to a named tuple, use the double-star-operator [#]_::
+
+ >>> d = {'x': 11, 'y': 22}
+ >>> Point(**d)
+ Point(x=11, y=22)
+
Since a named tuple is a regular Python class, it is easy to add or change
functionality. For example, the display format can be changed by overriding
the :meth:`__repr__` method:
@@ -520,5 +525,5 @@
.. rubric:: Footnotes
-.. [#] For information on the star-operator see
+.. [#] For information on the double-star-operator see
:ref:`tut-unpacking-arguments` and :ref:`calls`.
diff --git a/Lib/collections.py b/Lib/collections.py
index 3d98f7c..c6d0d0f 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -62,6 +62,7 @@
__slots__ = () \n
def __new__(cls, %(argtxt)s):
return tuple.__new__(cls, (%(argtxt)s)) \n
+ _cast = classmethod(tuple.__new__) \n
def __repr__(self):
return '%(typename)s(%(reprtxt)s)' %% self \n
def _asdict(t):
@@ -69,7 +70,7 @@
return {%(dicttxt)s} \n
def _replace(self, **kwds):
'Return a new %(typename)s object replacing specified fields with new values'
- return %(typename)s(*map(kwds.get, %(field_names)r, self)) \n
+ return %(typename)s._cast(map(kwds.get, %(field_names)r, self)) \n
@property
def _fields(self):
return %(field_names)r \n\n''' % locals()
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 73ae62a..edffbbe 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -46,6 +46,7 @@
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._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
@@ -90,12 +91,14 @@
def test_odd_sizes(self):
Zero = namedtuple('Zero', '')
self.assertEqual(Zero(), ())
+ self.assertEqual(Zero._cast([]), ())
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(1).d, 1)
self.assertEqual(repr(Dot(1)), 'Dot(d=1)')
self.assertEqual(Dot(1)._asdict(), {'d':1})
@@ -108,6 +111,7 @@
Big = namedtuple('Big', names)
b = Big(*range(n))
self.assertEqual(b, tuple(range(n)))
+ self.assertEqual(Big._cast(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