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`.