[Dynamic Language] Python Tips

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Python Slicing 序列切片

In [1]: l = [1,2,3,4]
In [2]: l[1:3]
Out[2]: [2, 3]

In [4]: l[1:]　//省略结束
Out[4]: [2, 3, 4]

In [5]: l[:2] //省略开始
Out[5]: [1, 2]

In [8]: l[::-1] //基数倒排序
Out[8]: [4, 3, 2, 1]

In [9]: l[::2] //基数取索引为偶数项
Out[9]: [1, 3]

In [9]: l[-2:] //取后两项
Out[9]: [ ３, ４]

Python 列表推导

l  = [1,2,3,4,5,6]
result1 = [x+1 for x in l]
相当于以下代码:
result2 = []
for x in l :
    result2.append(x+1)


result3 = [x+1 for x in l if x > 3]
相当于以下代码:
result4 = []
for x in l:
    if x > 3:
        result4.append(x+1)


l2 = [4,5,6]
result5 = [x+y for x in l if x>4 for y in l2 if y>5]
相当于以下代码:
result6 = []
for x in l:
    if x > 4:
        for y in l2:
            if y > 5:
                result6.append(x+y)

字典转化

In [11]: l = [(1,2), (3,4),(5,6)]

In [12]: d = dict(l)

In [13]: d
Out[13]: {1: 2, 3: 4, 5: 6}

转化为10进制数

In [45]: int("101", 2)
Out[45]: 5

In [46]: int("10", 8)
Out[46]: 8

In [47]: int("0xa", 16)
Out[47]: 10

all 、any

In [6]: print all( x > -1 for x in range(10))
True

In [7]: print all( x > 1 for x in range(10))
False

In [9]: print any( x > 1 for x in range(10))
True

In [10]: print any( x > 11 for x in range(10))
False

一行代码求字符串中字串的个数

In [14]: "abcaba".count('a')
Out[14]: 3

一行代码求列表的乘积

In [16]: reduce(lambda x,y: x*y, [1,2,3])
Out[16]: 6