python之列表和元组

列表 mutable

操作符：
标准类型操作符都适用

序列类型操作符：
slice 、in 略
+ ：

>>> lis1 = ['hello']
>>> lis2= ['world']
>>> lis1 + lis2
['hello', 'world']

*:

>>> lis = ['hello', 'world']
>>> lis * 2
['hello', 'world', 'hello', 'world']

内建函数

标准类型内建函数都适用

序列内建函数介绍几个：
sum：

>>> sum([3, 4])
7
>>> sum([3, 4], 5)
12

max and min：

>>> max([3, 4])
4
>>> min([3, 4])
3

zip:

>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> zipped
[(1, 4), (2, 5), (3, 6)]
>>> x2, y2 = zip(*zipped)
>>> x == list(x2) and y == list(y2)
True

enumerate：

>>> for i, j in enumerate(['hello', 'world']):
print i, j
0 hello
1 world 

list and tuple：

>>> tuple([3, 4])
(3, 4)
>>> list((3, 4))
[3, 4]

列表内建函数

list.append(x)
list.extend(lis)
list.insert(i, x)
list.remove(x)
list.pop(i) #会同时返回移除的值，如果没有设置i，则返回最后一个值
del list[i]   del list[i:j]
list.index(x) #返回x第一次出现的位置
list.count(x) #返回x出现的次数
list.sort() #sorted() 见 sort高级用法
list.reverse()

#list快速创建：
lis = [x**2 for x in range(10)]

[(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
-----------------------------------
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

matrix = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
[[row[i] for row in matrix] for i in range(4)]
------------------------------------
[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]

sort高级用法

both list.sort() and sorted() added a key parameter to specify a FUNCTION to be called on each list element prior to making comparisons.

而且通过通过设置reverse可以颠倒排序结果

#注意key后的是function，不是function call的值, 所以常用lambda表达式
sorted("This is a test string".split(), key=str.lower)
----------------------------------------
['This', 'test', 'string', 'is', 'a']

#A common pattern is to sort complex objects using some of the object’s indices as keys
student_tuples = [('john', 'A', 15),('jane', 'B', 12),('dave', 'B', 10),]
sorted(student_tuples, key=lambda student: student[2])
----------------------------------------
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

#The same technique works for objects with named attributes
class Student(object):
    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),]
sorted(student_objects, key=lambda student: student.age)
------------------------------------------
[('Dave', 'B', 10), ('Jane', 'B', 12), ('John', 'A', 15)]

#上面都可以一些python内置的函数
from operator import itemgetter, attrgetter
sorted(student_tuples, key=itemgetter(2))
sorted(student_objects, key=attrgetter('age'))
sorted(student_tuples, key=itemgetter(1,2))
sorted(student_objects, key=attrgetter('grade', 'age'))

 

浅拷贝与深拷贝 

浅拷贝只拷贝壳，并没有拷贝内容

import copy

class Foo(object):
    def __init__(self, val):
         self.val = val

    def __repr__(self):
        return str(self.val)

foo = Foo(1)

a = ['foo', foo]
b = a[:]
c = list(a)
d = copy.copy(a)
e = copy.deepcopy(a)

# edit orignal list and instance 
a.append('baz')
foo.val = 5

print "original: %r
 slice: %r
 list(): %r
 copy: %r
 deepcopy: %r" 
       % (a, b, c, d, e)

-----------------------------------------
original: ['foo', 5, 'baz']
slice: ['foo', 5]
list(): ['foo', 5]
copy: ['foo', 5]
deepcopy: ['foo', 1]

元组 immutable

 因为列表mutable，元组immutable， 所有元组可作字典key，而列表不行。

 

2015-05-25