30个有关Python的小技巧

从我开始学习python的时候，我就开始自己总结一个python小技巧的集合。后来当我什么时候在Stack Overflow或者在某个开源软件里看到一段很酷代码的时候，我就很惊讶：原来还能这么做！，当时我会努力的自己尝试一下这段代码，直到我懂了它的整体思路以后，我就把这段代码加到我的集合里。这篇博客其实就是这个集合整理后一部分的公开亮相。如果你已经是个python大牛，那么基本上你应该知道这里面的大多数用法了，但我想你应该也能发现一些你不知道的新技巧。而如果你之前是一个c,c++,java的程序员 ，同时在学习python，或者干脆就是一个刚刚学习编程的新手，那么你应该会看到很多特别有用能让你感到惊奇的实用技巧，就像我当初一样。

每一个技巧和语言用法都会在一个个实例中展示给大家，也不需要有其他的说明。我已经尽力把每个例子弄的通俗易懂，但是因为读者对python的熟悉程度不同，仍然可能难免有一些晦涩的地方。所以如果这些例子本身无法让你读懂，至少这个例子的标题在你后面去google搜索的时候会帮到你。

整个集合大概是按照难易程度排序，简单常见的在前面，比较少见的在最后。

 

1.1 拆箱

 

>>> a, b,c = 1, 2, 3

>>> a, b,c

(1, 2, 3)

>>> a, b,c = [1, 2, 3]

>>> a, b,c

(1, 2, 3)

>>> a, b,c = (2 * i + 1 for i in range(3))

>>> a, b,c

(1, 3, 5)

>>> a, (b,c), d = [1, (2, 3), 4]

>>> a

1

>>> b

2

>>> c

3

>>> d

4

1.2 拆箱变量交换

 

>>> a, b =1, 2

>>> a, b =b, a

>>> a, b

(2, 1)

1.3 扩展拆箱（只兼容python3）

 

>>> a, *b,c = [1, 2, 3, 4, 5]

>>> a

1

>>> b

[2, 3, 4]

>>> c

5

1.4 负数索引

 

>>> a =[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> a[-1]

10

>>> a[-3]

8

1.5 切割列表

 

>>> a =[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> a[2:8]

[2, 3, 4, 5, 6, 7]

1.6 负数索引切割列表

 

>>> a =[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>>a[-4:-2]

[7, 8]

1.7指定步长切割列表

 

>>> a =[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> a[::2]

[0, 2, 4, 6, 8, 10]

>>> a[::3]

[0, 3, 6, 9]

>>>a[2:8:2]

[2, 4, 6]

1.8 负数步长切割列表

 

>>> a =[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>>a[::-1]

[10, 9, 8, 7, 6, 5,4, 3, 2, 1, 0]

>>>a[::-2]

[10, 8, 6, 4, 2, 0]

1.9 列表切割赋值

 

>>> a =[1, 2, 3, 4, 5]

>>> a[2:3]= [0, 0]

>>> a

[1, 2, 0, 0, 4, 5]

>>> a[1:1]= [8, 9]

>>> a

[1, 8, 9, 2, 0, 0,4, 5]

>>>a[1:-1] = []

>>> a

[1, 5]

1.10 命名列表切割方式

 

>>> a =[0, 1, 2, 3, 4, 5]

>>>LASTTHREE = slice(-3, None)

>>>LASTTHREE

slice(-3, None,None)

>>>a[LASTTHREE]

[3, 4, 5]

1.11 列表以及迭代器的压缩和解压缩

 

>>> a =[1, 2, 3]

>>> b =['a', 'b', 'c']

>>> z =zip(a, b)

>>> z

[(1, 'a'), (2,'b'), (3, 'c')]

>>>zip(*z)

[(1, 2, 3), ('a','b', 'c')]

1.12 列表相邻元素压缩器

 

>>> a =[1, 2, 3, 4, 5, 6]

>>>zip(*([iter(a)] * 2))

[(1, 2), (3, 4),(5, 6)]

 

>>>group_adjacent = lambda a, k: zip(*([iter(a)] * k))

>>>group_adjacent(a, 3)

[(1, 2, 3), (4, 5,6)]

>>>group_adjacent(a, 2)

[(1, 2), (3, 4),(5, 6)]

>>>group_adjacent(a, 1)

[(1,), (2,), (3,),(4,), (5,), (6,)]

 

>>>zip(a[::2], a[1::2])

[(1, 2), (3, 4),(5, 6)]

 

>>>zip(a[::3], a[1::3], a[2::3])

[(1, 2, 3), (4, 5,6)]

 

>>>group_adjacent = lambda a, k: zip(*(a[i::k] for i in range(k)))

>>>group_adjacent(a, 3)

[(1, 2, 3), (4, 5,6)]

>>>group_adjacent(a, 2)

[(1, 2), (3, 4),(5, 6)]

>>>group_adjacent(a, 1)

[(1,), (2,), (3,),(4,), (5,), (6,)]

1.13 在列表中用压缩器和迭代器滑动取值窗口

 

>>> defn_grams(a, n):

...     z = [iter(a[i:]) for i in range(n)]

...     return zip(*z)

...

>>> a =[1, 2, 3, 4, 5, 6]

>>>n_grams(a, 3)

[(1, 2, 3), (2, 3,4), (3, 4, 5), (4, 5, 6)]

>>>n_grams(a, 2)

[(1, 2), (2, 3),(3, 4), (4, 5), (5, 6)]

>>>n_grams(a, 4)

[(1, 2, 3, 4), (2,3, 4, 5), (3, 4, 5, 6)]

1.14 用压缩器反转字典

 

>>> m ={'a': 1, 'b': 2, 'c': 3, 'd': 4}

>>>m.items()

[('a', 1), ('c',3), ('b', 2), ('d', 4)]

>>>zip(m.values(), m.keys())

[(1, 'a'), (3,'c'), (2, 'b'), (4, 'd')]

>>> mi =dict(zip(m.values(), m.keys()))

>>> mi

{1: 'a', 2: 'b', 3:'c', 4: 'd'}

1.15 列表展开

 

>>> a =[[1, 2], [3, 4], [5, 6]]

>>>list(itertools.chain.from_iterable(a))

[1, 2, 3, 4, 5, 6]

 

>>> sum(a,[])

[1, 2, 3, 4, 5, 6]

 

>>> [x forl in a for x in l]

[1, 2, 3, 4, 5, 6]

 

>>> a =[[[1, 2], [3, 4]], [[5, 6], [7, 8]]]

>>> [x forl1 in a for l2 in l1 for x in l2]

[1, 2, 3, 4, 5, 6,7, 8]

 

>>> a =[1, 2, [3, 4], [[5, 6], [7, 8]]]

>>>flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else[x]

>>>flatten(a)

[1, 2, 3, 4, 5, 6,7, 8]

1.16 生成器表达式

 

>>> g = (x** 2 for x in xrange(10))

>>>next(g)

0

>>>next(g)

1

>>>next(g)

4

>>>next(g)

9

>>> sum(x** 3 for x in xrange(10))

2025

>>> sum(x** 3 for x in xrange(10) if x % 3 == 1)

408

1.17 字典推导

 

>>> m ={x: x ** 2 for x in range(5)}

>>> m

{0: 0, 1: 1, 2: 4,3: 9, 4: 16}

 

>>> m ={x: 'A' + str(x) for x in range(10)}

>>> m

{0: 'A0', 1: 'A1',2: 'A2', 3: 'A3', 4: 'A4', 5: 'A5', 6: 'A6', 7: 'A7', 8: 'A8', 9: 'A9'}

1.18 用字典推导反转字典

 

>>> m ={'a': 1, 'b': 2, 'c': 3, 'd': 4}

>>> m

{'d': 4, 'a': 1,'b': 2, 'c': 3}

>>> {v: kfor k, v in m.items()}

{1: 'a', 2: 'b', 3:'c', 4: 'd'}

1.19 命名元组

 

>>> Point= collections.namedtuple('Point', ['x', 'y'])

>>> p =Point(x=1.0, y=2.0)

>>> p

Point(x=1.0, y=2.0)

>>> p.x

1.0

>>> p.y

2.0

1.20 继承命名元组

 

>>> classPoint(collections.namedtuple('PointBase', ['x', 'y'])):

...     __slots__ = ()

...     def __add__(self, other):

...             return Point(x=self.x + other.x,y=self.y + other.y)

...

>>> p =Point(x=1.0, y=2.0)

>>> q =Point(x=2.0, y=3.0)

>>> p + q

Point(x=3.0, y=5.0)

1.21 操作集合

 

>>> A ={1, 2, 3, 3}

>>> A

set([1, 2, 3])

>>> B ={3, 4, 5, 6, 7}

>>> B

set([3, 4, 5, 6,7])

>>> A | B

set([1, 2, 3, 4, 5,6,

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