以下是我长久以来收集的一些Python实用技巧和工具,希望能对刚学习Python的新手有所帮助。

1.交换变量

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

2.if 语句在行内

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

3.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cool。

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

4.数字技巧

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

5.注意浮点数的除法

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

6.数值比较

这是我见过诸多语言中很少有的如此棒的简便法

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

7.同时迭代两个列表

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

>>> Packers vs. Ravens
>>> 49ers vs. Patriots

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8.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

9.列表推导式

已知一个列表,我们可以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)

转变成如下:

numbers = [1,2,3,4,5,6]
even = [number for number in numbers if number%2 == 0]

是不是很牛呢,哈哈。

10.字典推导

和列表推导类似,字典可以做同样的工作:

teams = ["Packers", "49ers", "Ravens", "Patriots"]
print {key: value for value, key in enumerate(teams)}
>>> {'49ers': 1, 'Ravens': 2, 'Patriots': 3, 'Packers': 0}

11.初始化列表的值

items = [0]*3
print items
>>> [0,0,0]
12.列表转换为字符串
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print ", ".join(teams)
>>> 'Packers, 49ers, Ravens, Patriots'

13.从字典中获取元素

我承认try/except代码并不雅致,不过这里有一种简单方法,尝试在字典中查找key,如果没有找到对应的alue将用第二个参数设为其变量值。

data = {'user': 1, 'name': 'Max', 'three': 4}
try:
   is_admin = data['admin']
except KeyError:
   is_admin = False
data = {'user': 1, 'name': 'Max', 'three': 4}
is_admin = data.get('admin', False)

14.获取列表的子集

有时,你只需要列表中的部分元素,这里是一些获取列表子集的方法。

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]

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