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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.
This commit is contained in:
Raymond Hettinger 2011-01-12 01:16:57 +00:00
parent fdf2925452
commit b436b6cabc
1 changed files with 39 additions and 38 deletions
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77
Doc/howto/sorting.rst
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@ -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:
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
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: