Users demand iterable input for named tuples. The author capitulates.

This commit is contained in:
Raymond Hettinger 2007-12-18 23:51:15 +00:00
parent 0a8143f646
commit 85dfcf3530
3 changed files with 28 additions and 18 deletions

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@ -391,6 +391,8 @@ Example::
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 @@ Example::
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 @@ by the :mod:`csv` or :mod:`sqlite3` modules::
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 @@ function:
>>> 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 @@ and customizing it with :meth:`_replace`:
.. rubric:: Footnotes
.. [#] For information on the star-operator see
.. [#] For information on the double-star-operator see
:ref:`tut-unpacking-arguments` and :ref:`calls`.

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@ -62,6 +62,7 @@ def namedtuple(typename, field_names, verbose=False):
__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 @@ def namedtuple(typename, field_names, verbose=False):
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()

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@ -46,6 +46,7 @@ class TestNamedTuple(unittest.TestCase):
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 @@ class TestNamedTuple(unittest.TestCase):
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 @@ class TestNamedTuple(unittest.TestCase):
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