Python初学者的17个技巧

以下是我在Python学习过程中，总结的一些小技巧。不对之处还希望大家指正。

交换变量

x = 6y = 5x, y = y, xprint x>>>5print y>>>6

if语句在行内

print "hello" if True else "World">>>Hello

连接

下面的最后一种方式在绑定两个不同类型的对象时显得很酷。

 nfc = ["Packers","49ers"] afc = ["Ravens ", " Patriots"] print nfc + afc>>> ['Packers', '49ers', 'Ravens', 'Patriots']print str(1) + "world">>> 1 worldprint '1' + "world">>>1 worldprint 1, "world">>>1 worldprint nfc ,1>>> ['Packers', '49ers'] 1

计算技巧

#向下取整print 5.0//2>>>2#2的5次方print 2**5>> 32

注意浮点数的除法

print .3/.1>>>2.9999999999999996print .3//.1>>>2.0

数值比较

x = 2if 3 > x > 1:    print x>>> 2if 1 < x > 0    print x>>> 2

两个列表同时迭代

nfc = ["Packers", "49ers"]afc = ["Ravens", "Patriots"]for teama, teamb in zip(nfc, afc):     print teama + "  vs ." + teamb>>> Packers vs. Ravens>>> 49ers vs. Patriots

带索引的列表迭代

teams = ["Packers", "49ers", "Ravens", "Patriots"]for index, team in enumerate(teams):     print index, team>>> 0 Packers>>> 1 49ers>>> 2 Ravens>>> 3 Patriots

列表推导

已知一个列表，刷选出偶数列表方法:

numbers = [1,2,3,4,5,6]even = []for number in numbers:     if number %2 == 0:            even.append(number)

用下面的代替

numbers = [1,2,3,4,5,6]even = [number for number in numbers ]

初始化列表的值

items = [0] * 3print items>>> [0,0,0]

将列表转换成字符串

teams = ["Packers", "49ers", "Ravens", "Patriots"]print",  ".join(teams)>>>'Packers,49ers,Ravens,Patriots'

获取子列表

x = [1,2,3,4,5,6]#前3个print x[:3]>>> [1,2,3]#中间4个print x[1:5]>>> [2,3,4,5]#最后3个print x [-3:]>>> [4,5,6]#奇数项print x[::2]>>> [1,3,5]#偶数项print x[1::2]>>> [2,4,6]

迭代工具

和collections库一样，还有一个库叫itertools。

from itertools import combinationsteams = ["Packers", "49ers", "Ravens", "Patriots"]for game in combinations (teams, 2):     print game>>> ('Packers','49ers')>>> ('Packers', 'Ravens' )>>> ('Packers', 'Patriots' )>>> ('49ers', 'Ravens' ) >>> ('49ers', 'Patriots' ) >>> ('Ravens', 'Patriots' ) 

在python中，True和False是全局变量，因此：

 

False = Trueif False:   print "Hello"else:   print "World">>>Hello