[Python-checkins] r59727 - in python/trunk: Doc/library/collections.rst Lib/collections.py Lib/test/test_collections.py

Sat Jan 5 02:35:44 CET 2008

Author: raymond.hettinger
Date: Sat Jan 5 02:35:43 2008
New Revision: 59727
Modified:
 python/trunk/Doc/library/collections.rst
 python/trunk/Lib/collections.py
 python/trunk/Lib/test/test_collections.py
Log:
Improve namedtuple's _cast() method with a docstring, new name, and error-checking.
Modified: python/trunk/Doc/library/collections.rst
==============================================================================

--- python/trunk/Doc/library/collections.rst	(original)
+++ python/trunk/Doc/library/collections.rst	Sat Jan 5 02:35:43 2008
@@ -393,7 +393,13 @@
 def __new__(cls, x, y):
 return tuple.__new__(cls, (x, y))
 
- _cast = classmethod(tuple.__new__)
+ @classmethod
+ def _make(cls, iterable):
+ 'Make a new Point object from a sequence or iterable'
+ result = tuple.__new__(cls, iterable)
+ if len(result) != 2:
+ raise TypeError('Expected 2 arguments, got %d' % len(result))
+ return result
 
 def __repr__(self):
 return 'Point(x=%r, y=%r)' % self
@@ -404,7 +410,7 @@
 
 def _replace(self, **kwds):
 'Return a new Point object replacing specified fields with new values'
- return self.__class__._cast(map(kwds.get, ('x', 'y'), self))
+ return self.__class__._make(map(kwds.get, ('x', 'y'), self))
 
 x = property(itemgetter(0))
 y = property(itemgetter(1))
@@ -426,34 +432,28 @@
 EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')
 
 import csv
- for emp in map(EmployeeRecord._cast, csv.reader(open("employees.csv", "rb"))):
+ for emp in map(EmployeeRecord._make, 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 map(EmployeeRecord._cast, cursor.fetchall()):
+ for emp in map(EmployeeRecord._make, cursor.fetchall()):
 print emp.name, emp.title
 
 In addition to the methods inherited from tuples, named tuples support
-three additonal methods and one attribute.
+three additional methods and one attribute.
 
-.. method:: namedtuple._cast(iterable)
+.. method:: namedtuple._make(iterable)
 
- Class method returning a new instance taking the positional arguments from the
- *iterable*. Useful for casting existing sequences and iterables to named tuples.
-
- This fast constructor does not check the length of the inputs. To achieve the
- same effect with length checking, use the star-operator instead.
+ Class method that makes a new instance from an existing sequence or iterable.
 
 ::
 
- >>> t = [11, 22]
- >>> Point._cast(t) # fast conversion
- Point(x=11, y=22)
- >>> Point(*t) # slow conversion with length checking
- Point(x=11, y=22)
+ >>> t = [11, 22]
+ >>> Point._make(t)
+ Point(x=11, y=22)
 
 .. method:: somenamedtuple._asdict()
 
Modified: python/trunk/Lib/collections.py
==============================================================================
--- python/trunk/Lib/collections.py	(original)
+++ python/trunk/Lib/collections.py	Sat Jan 5 02:35:43 2008
@@ -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:
Modified: python/trunk/Lib/test/test_collections.py
==============================================================================
--- python/trunk/Lib/test/test_collections.py	(original)
+++ python/trunk/Lib/test/test_collections.py	Sat Jan 5 02:35:43 2008
@@ -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
