diff options
| -rw-r--r-- | Doc/howto/sorting.rst | 13 | ||||
| -rw-r--r-- | Doc/library/stdtypes.rst | 3 |
2 files changed, 14 insertions, 2 deletions
diff --git a/Doc/howto/sorting.rst b/Doc/howto/sorting.rst index 1280446..b2fccb1 100644 --- a/Doc/howto/sorting.rst +++ b/Doc/howto/sorting.rst @@ -145,6 +145,17 @@ ascending *age*, do the *age* sort first and then sort again using *grade*: >>> sorted(s, key=attrgetter('grade'), reverse=True) # now sort on primary key, descending [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)] +This can be abstracted out into a wrapper function that can take a list and +tuples of field and order to sort them on multiple passes. + + >>> def multisort(xs, specs): + ... for key, reverse in reversed(specs): + ... xs.sort(key=attrgetter(key), reverse=reverse) + ... return xs + + >>> multisort(list(student_objects), (('grade', True), ('age', False))) + [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)] + The `Timsort <https://en.wikipedia.org/wiki/Timsort>`_ algorithm used in Python does multiple sorts efficiently because it can take advantage of any ordering already present in a dataset. @@ -246,7 +257,7 @@ To convert to a key function, just wrap the old comparison function: .. testsetup:: - from functools import cmp_to_key + >>> from functools import cmp_to_key .. doctest:: diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst index d0d5c61..01fb5d5 100644 --- a/Doc/library/stdtypes.rst +++ b/Doc/library/stdtypes.rst @@ -1201,6 +1201,8 @@ application). --- this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade). + For sorting examples and a brief sorting tutorial, see :ref:`sortinghowto`. + .. impl-detail:: While a list is being sorted, the effect of attempting to mutate, or even @@ -4752,4 +4754,3 @@ types, where they are relevant. Some of these are not reported by the .. [5] To format only a tuple you should therefore provide a singleton tuple whose only element is the tuple to be formatted. - |