mirror of https://github.com/python/cpython
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.
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@ -4,6 +4,7 @@ Sorting HOW TO
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**************
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:Author: Andrew Dalke and Raymond Hettinger
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:Release: 0.1
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Python lists have a built-in :meth:`list.sort` method that modifies the list
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@ -17,7 +18,7 @@ Sorting Basics
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==============
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A simple ascending sort is very easy: just call the :func:`sorted` function. It
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returns a new sorted list:
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returns a new sorted list::
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>>> sorted([5, 2, 3, 1, 4])
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[1, 2, 3, 4, 5]
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@ -57,28 +58,28 @@ A common pattern is to sort complex objects using some of the object's indices
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as keys. For example:
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>>> student_tuples = [
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... ('john', 'A', 15),
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... ('jane', 'B', 12),
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... ('dave', 'B', 10),
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... ]
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('john', 'A', 15),
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('jane', 'B', 12),
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('dave', 'B', 10),
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]
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>>> sorted(student_tuples, key=lambda student: student[2]) # sort by age
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[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
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The same technique works for objects with named attributes. For example:
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>>> class Student:
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... def __init__(self, name, grade, age):
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... self.name = name
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... self.grade = grade
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... self.age = age
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... def __repr__(self):
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... return repr((self.name, self.grade, self.age))
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def __init__(self, name, grade, age):
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self.name = name
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self.grade = grade
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self.age = age
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def __repr__(self):
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return repr((self.name, self.grade, self.age))
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>>> student_objects = [
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... Student('john', 'A', 15),
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... Student('jane', 'B', 12),
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... Student('dave', 'B', 10),
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... ]
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Student('john', 'A', 15),
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Student('jane', 'B', 12),
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Student('dave', 'B', 10),
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]
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>>> sorted(student_objects, key=lambda student: student.age) # sort by age
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[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
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@ -207,39 +208,39 @@ return a negative value for less-than, return zero if they are equal, or return
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a positive value for greater-than. For example, we can do:
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>>> def numeric_compare(x, y):
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... return x - y
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>>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare) # doctest: +SKIP
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return x - y
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>>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare)
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[1, 2, 3, 4, 5]
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Or you can reverse the order of comparison with:
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>>> def reverse_numeric(x, y):
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... return y - x
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>>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric) # doctest: +SKIP
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return y - x
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>>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric)
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[5, 4, 3, 2, 1]
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When porting code from Python 2.x to 3.x, the situation can arise when you have
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the user supplying a comparison function and you need to convert that to a key
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function. The following wrapper makes that easy to do:
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function. The following wrapper makes that easy to do::
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>>> def cmp_to_key(mycmp):
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... 'Convert a cmp= function into a key= function'
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... class K(object):
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... def __init__(self, obj, *args):
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... self.obj = obj
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... def __lt__(self, other):
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... return mycmp(self.obj, other.obj) < 0
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... def __gt__(self, other):
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... return mycmp(self.obj, other.obj) > 0
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... def __eq__(self, other):
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... return mycmp(self.obj, other.obj) == 0
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... def __le__(self, other):
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... return mycmp(self.obj, other.obj) <= 0
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... def __ge__(self, other):
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... return mycmp(self.obj, other.obj) >= 0
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... def __ne__(self, other):
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... return mycmp(self.obj, other.obj) != 0
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... return K
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def cmp_to_key(mycmp):
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'Convert a cmp= function into a key= function'
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class K(object):
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def __init__(self, obj, *args):
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self.obj = obj
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def __lt__(self, other):
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return mycmp(self.obj, other.obj) < 0
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def __gt__(self, other):
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return mycmp(self.obj, other.obj) > 0
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def __eq__(self, other):
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return mycmp(self.obj, other.obj) == 0
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def __le__(self, other):
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return mycmp(self.obj, other.obj) <= 0
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def __ge__(self, other):
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return mycmp(self.obj, other.obj) >= 0
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def __ne__(self, other):
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return mycmp(self.obj, other.obj) != 0
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return K
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To convert to a key function, just wrap the old comparison function:
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