http://hg.python.org/cpython/rev/22e514e41fac changeset: 87607:22e514e41fac branch: 3.3 parent: 87605:bab7dc2ffc16 user: Benjamin Peterson <benjamin@python.org> date: Tue Nov 26 23:05:25 2013 -0600 summary: recommend OrderedDict for this FAQ (closes #19805) files: Doc/faq/programming.rst | 30 ++-------------------------- 1 files changed, 3 insertions(+), 27 deletions(-) diff --git a/Doc/faq/programming.rst b/Doc/faq/programming.rst --- a/Doc/faq/programming.rst +++ b/Doc/faq/programming.rst @@ -1193,34 +1193,10 @@ Dictionaries ============ -How can I get a dictionary to display its keys in a consistent order? ---------------------------------------------------------------------- +How can I get a dictionary to store and display its keys in a consistent order? +------------------------------------------------------------------------------- -You can't. Dictionaries store their keys in an unpredictable order, so the -display order of a dictionary's elements will be similarly unpredictable. - -This can be frustrating if you want to save a printable version to a file, make -some changes and then compare it with some other printed dictionary. In this -case, use the ``pprint`` module to pretty-print the dictionary; the items will -be presented in order sorted by the key. - -A more complicated solution is to subclass ``dict`` to create a -``SortedDict`` class that prints itself in a predictable order. Here's one -simpleminded implementation of such a class:: - - class SortedDict(dict): - def __repr__(self): - keys = sorted(self.keys()) - result = ("{!r}: {!r}".format(k, self[k]) for k in keys) - return "{{{}}}".format(", ".join(result)) - - __str__ = __repr__ - -This will work for many common situations you might encounter, though it's far -from a perfect solution. The largest flaw is that if some values in the -dictionary are also dictionaries, their values won't be presented in any -particular order. - +Use :class:`collections.OrderedDict`. I want to do a complicated sort: can you do a Schwartzian Transform in Python? ------------------------------------------------------------------------------ -- Repository URL: http://hg.python.org/cpython