Python 随想一些有用feature

#coding=gbk
import os #operating system
import sys #system
import copy
from pprint import pprint #perfect print 
from operator import attrgetter

a = [1, 2, 3, 4, 5]
b = [6, 7, 8, 9, 10]

#python使用引用计数
c = a

print c
#[1, 2, 3, 4, 5]

c[0] = -1
print c
#[-1, 2, 3, 4, 5]
print a
#[-1, 2, 3, 4, 5]

a[0] = 1
print c
#[1, 2, 3, 4, 5]
print a
#[1, 2, 3, 4, 5]

#打包zip函数：
for i,j in zip(a, b):
    print i, j
    
#输出    
#1 6
#2 7
#3 8
#4 9
#5 10

#字典dict:
d ={}
for i,j in zip(a, b):
    d[i] = j #d[key] = value
    
pprint(d)
#{1: 6, 2: 7, 3: 8, 4: 9, 5: 10} 

#python使用引用计数，使用深度copy

d[1233] = {11111111111:copy.deepcopy(d)}
pprint(d)
#{1: 6,
# 2: 7,
# 3: 8,
# 4: 9,
# 5: 10,
# 1233: {11111111111L: {1: 6, 2: 7, 3: 8, 4: 9, 5: 10}}}

#链表list:
print sum(a)#15
print len(a)#5
print [2 * x for x in a]#[2, 4, 6, 8, 10] 列表解析
print a+b #[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

#string:
print "&".join([str(x) for x in a])#1&2&3&4&5
print "1&2&3&4&5".split("&")#['1', '2', '3', '4', '5']
print len("abc")#3

#文件
fileName = "test.py"
for line in file(fileName):
    line = line.strip().split("\t")

#eval 函数，可以解析字符串形式的python数据
print type(eval("[1,2]"))#<type 'list'>
print type(eval("{1:2}"))#<type 'dict'>

#os
print os.listdir(".")#显示dir的所有项
print dir(os)#输出os module的所有方法
print help(os)#输出os模块的help doc string

#二级排序（基于python sort是稳定的排序）This wonderful property lets you build complex sorts in a series of sorting steps. For example, to sort the student data by descending grade and then ascending age, do the age sort first and then sort again using grade: 
class student:
    def __init__(self, a, g):
        self.age = a
        self.grade = g
    def __str__(self):
        return "age=%d,grade=%d"%(self.age, self.grade)
    
student_objects = [student(10, 2),student(3, 40)]

s = sorted(student_objects, key=attrgetter('age'))     # sort on age key
sorted(s, key=attrgetter('grade'), reverse=True)       # now sort on grape key, descending

print [str(x) for x in s]

sys.exit(0)