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Docs on named tuple's naming conventions and limits of subclassing

This commit is contained in:
Raymond Hettinger 2008-01-08 02:24:15 +00:00
parent 581671419f
commit ac5742e0fe
1 changed files with 7 additions and 1 deletions
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Doc/library/collections.rst
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@ -446,7 +446,8 @@ by the :mod:`csv` or :mod:`sqlite3` modules::
print emp.name, emp.title
In addition to the methods inherited from tuples, named tuples support
three additional methods and one attribute.
three additional methods and one attribute. To prevent conflicts with
field names, the method and attribute names start with an underscore.
.. method:: somenamedtuple._make(iterable)
@ -533,6 +534,11 @@ faster versions that bypass error-checking and that localize variable access::
def _replace(self, _map=map, **kwds):
return self._make(_map(kwds.get, ('x', 'y'), self))
Subclassing is not useful for adding new, stored fields. Instead, simply
create a new named tuple type from the :attr:`_fields` attribute::
>>> Pixel = namedtuple('Pixel', Point._fields + Color._fields)
Default values can be implemented by using :meth:`_replace` to
customize a prototype instance::