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author | Raymond Hettinger <python@rcn.com> | 2011-01-12 01:16:57 (GMT) |
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committer | Raymond Hettinger <python@rcn.com> | 2011-01-12 01:16:57 (GMT) |
commit | b436b6cabcd35d4bcb75245211be9b40bc0198f5 (patch) | |
tree | 84731acdabfab4f4988329cf0d1fed11ac877a3d /Doc/howto/sorting.rst | |
parent | fdf29254521cd49c06312195d734c2061706fafb (diff) | |
download | cpython-b436b6cabcd35d4bcb75245211be9b40bc0198f5.zip cpython-b436b6cabcd35d4bcb75245211be9b40bc0198f5.tar.gz cpython-b436b6cabcd35d4bcb75245211be9b40bc0198f5.tar.bz2 |
Revert r87946. The virtues of readability and of examples that
can be cut and pasted are more important than having a doctests
on examples that already work.
Diffstat (limited to 'Doc/howto/sorting.rst')
-rw-r--r-- | Doc/howto/sorting.rst | 79 |
1 files changed, 40 insertions, 39 deletions
diff --git a/Doc/howto/sorting.rst b/Doc/howto/sorting.rst index af1149d..134c9ce 100644 --- a/Doc/howto/sorting.rst +++ b/Doc/howto/sorting.rst @@ -4,6 +4,7 @@ Sorting HOW TO ************** :Author: Andrew Dalke and Raymond Hettinger +:Release: 0.1 Python lists have a built-in :meth:`list.sort` method that modifies the list @@ -17,7 +18,7 @@ Sorting Basics ============== A simple ascending sort is very easy: just call the :func:`sorted` function. It -returns a new sorted list: +returns a new sorted list:: >>> sorted([5, 2, 3, 1, 4]) [1, 2, 3, 4, 5] @@ -57,28 +58,28 @@ A common pattern is to sort complex objects using some of the object's indices as keys. For example: >>> student_tuples = [ - ... ('john', 'A', 15), - ... ('jane', 'B', 12), - ... ('dave', 'B', 10), - ... ] + ('john', 'A', 15), + ('jane', 'B', 12), + ('dave', 'B', 10), + ] >>> sorted(student_tuples, key=lambda student: student[2]) # sort by age [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)] The same technique works for objects with named attributes. For example: >>> class Student: - ... def __init__(self, name, grade, age): - ... self.name = name - ... self.grade = grade - ... self.age = age - ... def __repr__(self): - ... return repr((self.name, self.grade, self.age)) + def __init__(self, name, grade, age): + self.name = name + self.grade = grade + self.age = age + def __repr__(self): + return repr((self.name, self.grade, self.age)) >>> student_objects = [ - ... Student('john', 'A', 15), - ... Student('jane', 'B', 12), - ... Student('dave', 'B', 10), - ... ] + Student('john', 'A', 15), + Student('jane', 'B', 12), + Student('dave', 'B', 10), + ] >>> sorted(student_objects, key=lambda student: student.age) # sort by age [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)] @@ -207,39 +208,39 @@ return a negative value for less-than, return zero if they are equal, or return a positive value for greater-than. For example, we can do: >>> def numeric_compare(x, y): - ... return x - y - >>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare) # doctest: +SKIP + return x - y + >>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare) [1, 2, 3, 4, 5] Or you can reverse the order of comparison with: >>> def reverse_numeric(x, y): - ... return y - x - >>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric) # doctest: +SKIP + return y - x + >>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric) [5, 4, 3, 2, 1] When porting code from Python 2.x to 3.x, the situation can arise when you have the user supplying a comparison function and you need to convert that to a key -function. The following wrapper makes that easy to do: - - >>> def cmp_to_key(mycmp): - ... 'Convert a cmp= function into a key= function' - ... class K(object): - ... def __init__(self, obj, *args): - ... self.obj = obj - ... def __lt__(self, other): - ... return mycmp(self.obj, other.obj) < 0 - ... def __gt__(self, other): - ... return mycmp(self.obj, other.obj) > 0 - ... def __eq__(self, other): - ... return mycmp(self.obj, other.obj) == 0 - ... def __le__(self, other): - ... return mycmp(self.obj, other.obj) <= 0 - ... def __ge__(self, other): - ... return mycmp(self.obj, other.obj) >= 0 - ... def __ne__(self, other): - ... return mycmp(self.obj, other.obj) != 0 - ... return K +function. The following wrapper makes that easy to do:: + + def cmp_to_key(mycmp): + 'Convert a cmp= function into a key= function' + class K(object): + def __init__(self, obj, *args): + self.obj = obj + def __lt__(self, other): + return mycmp(self.obj, other.obj) < 0 + def __gt__(self, other): + return mycmp(self.obj, other.obj) > 0 + def __eq__(self, other): + return mycmp(self.obj, other.obj) == 0 + def __le__(self, other): + return mycmp(self.obj, other.obj) <= 0 + def __ge__(self, other): + return mycmp(self.obj, other.obj) >= 0 + def __ne__(self, other): + return mycmp(self.obj, other.obj) != 0 + return K To convert to a key function, just wrap the old comparison function: |