cpython: 22e514e41fac (original) (raw)

Mercurial > cpython

changeset 87607:22e514e41fac 3.3

recommend OrderedDict for this FAQ (closes #19805) [#19805]

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--- a/Doc/faq/programming.rst +++ b/Doc/faq/programming.rst @@ -1193,34 +1193,10 @@ that final assignment still results in a Dictionaries ============ -How can I get a dictionary to 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. +How can I get a dictionary to store and display its keys in a consistent order? +------------------------------------------------------------------------------- -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):[](#l1.25)

•       keys = sorted(self.keys())[](#l1.26)

•       result = ("{!r}: {!r}".format(k, self[k]) for k in keys)[](#l1.27)

•       return "{{{}}}".format(", ".join(result))[](#l1.28)

-

•   __str__ = __repr__[](#l1.30)

- -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? ------------------------------------------------------------------------------