<编程技巧> 18个常用技巧

戴宇轩

1. 拆箱

1. >>> a, b, c = 1, 2, 3
   
2. >>> a, b, c
   
3. (1, 2, 3)
   
4. >>> a, b, c = [1, 2, 3]
   
5. >>> a, b, c
   
6. (1, 2, 3)
   
7. >>> a, b, c = (2 * i + 1 for i in range(3))
   
8. >>> a, b, c
   
9. (1, 3, 5)
   
10. >>> a, (b, c), d = [1, (2, 3), 4]
    
11. >>> a
    
12. 1
    
13. >>> b
    
14. 2
    
15. >>> c
    
16. 3
    
17. >>> d
    
18. 4

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2. 变量交换

1. >>> a, b = 1, 2
   
2. >>> a, b = b, a
   
3. >>> a, b
   
4. (2, 1)

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3. 扩展拆箱(只兼容python3)

1. >>> a, *b, c = [1, 2, 3, 4, 5]
   
2. >>> a
   
3. 1
   
4. >>> b
   
5. [2, 3, 4]
   
6. >>> c
   
7. 5

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4. 负数索引

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

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5. 切割列表

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

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6. 负数索引切割列表

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

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7. 指定步长切割列表

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

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8. 负数步长切割列表

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

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9. 列表切割赋值

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

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10. 命名列表切割方式

1. >>> a = [0, 1, 2, 3, 4, 5]
   
2. >>> cut = slice(-3, None)
   
3. >>> cut
   
4. slice(-3, None, None)
   
5. >>> a[cut]
   
6. [3, 4, 5]

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11. 列表以及迭代器的压缩和解压缩

1. >>> a = [1, 2, 3]
   
2. >>> b = ['a', 'b', 'c']
   
3. >>> z = zip(a, b)
   
4. >>> z
   
5. [(1, 'a'), (2, 'b'), (3, 'c')]
   
6. >>> zip(*z)
   
7. [(1, 2, 3), ('a', 'b', 'c')]

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12. 列表相邻元素压缩器

1. >>> a = [1, 2, 3, 4, 5, 6]
   
2. >>> zip(*([iter(a)] * 2))
   
3. [(1, 2), (3, 4), (5, 6)]
   
4. 
   
5. >>> group_adjacent = lambda a, k: zip(*([iter(a)] * k))
   
6. >>> group_adjacent(a, 3)
   
7. [(1, 2, 3), (4, 5, 6)]
   
8. >>> group_adjacent(a, 2)
   
9. [(1, 2), (3, 4), (5, 6)]
   
10. >>> group_adjacent(a, 1)
    
11. [(1,), (2,), (3,), (4,), (5,), (6,)]
    
12. 
    
13. >>> zip(a[::2], a[1::2])
    
14. [(1, 2), (3, 4), (5, 6)]
    
15. 
    
16. >>> zip(a[::3], a[1::3], a[2::3])
    
17. [(1, 2, 3), (4, 5, 6)]
    
18. 
    
19. >>> group_adjacent = lambda a, k: zip(*(a[i::k] for i in range(k)))
    
20. >>> group_adjacent(a, 3)
    
21. [(1, 2, 3), (4, 5, 6)]
    
22. >>> group_adjacent(a, 2)
    
23. [(1, 2), (3, 4), (5, 6)]
    
24. >>> group_adjacent(a, 1)
    
25. [(1,), (2,), (3,), (4,), (5,), (6,)]

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13. 在列表中用压缩器和迭代器滑动取值窗口

1. >>> def n_grams(a, n):
   
2. ...     z = [iter(a[i:]) for i in range(n)]
   
3. ...     return zip(*z)
   
4. ...
   
5. >>> a = [1, 2, 3, 4, 5, 6]
   
6. >>> n_grams(a, 3)
   
7. [(1, 2, 3), (2, 3, 4), (3, 4, 5), (4, 5, 6)]
   
8. >>> n_grams(a, 2)
   
9. [(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
   
10. >>> n_grams(a, 4)
    
11. [(1, 2, 3, 4), (2, 3, 4, 5), (3, 4, 5, 6)]

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14. 用压缩器反转字典

1. >>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
   
2. >>> m.items()
   
3. [('a', 1), ('c', 3), ('b', 2), ('d', 4)]
   
4. >>> zip(m.values(), m.keys())
   
5. [(1, 'a'), (3, 'c'), (2, 'b'), (4, 'd')]
   
6. >>> mi = dict(zip(m.values(), m.keys()))
   
7. >>> mi
   
8. {1: 'a', 2: 'b', 3: 'c', 4: 'd'}

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15. 列表展开

1. >>> a = [[1, 2], [3, 4], [5, 6]]
   
2. >>> list(itertools.chain.from_iterable(a))
   
3. [1, 2, 3, 4, 5, 6]
   
4. 
   
5. >>> sum(a, [])
   
6. [1, 2, 3, 4, 5, 6]
   
7. 
   
8. >>> [x for l in a for x in l]
   
9. [1, 2, 3, 4, 5, 6]
   
10. 
    
11. >>> a = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
    
12. >>> [x for l1 in a for l2 in l1 for x in l2]
    
13. [1, 2, 3, 4, 5, 6, 7, 8]
    
14. 
    
15. >>> a = [1, 2, [3, 4], [[5, 6], [7, 8]]]
    
16. >>> flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]
    
17. >>> flatten(a)
    
18. [1, 2, 3, 4, 5, 6, 7, 8]

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16. 生成器表达式

1. >>> g = (x ** 2 for x in xrange(10))
   
2. >>> next(g)
   
3. 0
   
4. >>> next(g)
   
5. 1
   
6. >>> next(g)
   
7. 4
   
8. >>> next(g)
   
9. 9
   
10. >>> sum(x ** 3 for x in xrange(10))
    
11. 2025
    
12. >>> sum(x ** 3 for x in xrange(10) if x % 3 == 1)
    
13. 408

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17. 字典推导

1. >>> m = {x: x ** 2 for x in range(5)}
   
2. >>> m
   
3. {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
   
4. 
   
5. >>> m = {x: 'A' + str(x) for x in range(10)}
   
6. >>> m
   
7. {0: 'A0', 1: 'A1', 2: 'A2', 3: 'A3', 4: 'A4', 5: 'A5', 6: 'A6', 7: 'A7', 8: 'A8', 9: 'A9'}

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18. 用字典推导反转字典

1. >>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
   
2. >>> m
   
3. {'d': 4, 'a': 1, 'b': 2, 'c': 3}
   
4. >>> {v: k for k, v in m.items()}
   
5. {1: 'a', 2: 'b', 3: 'c', 4: 'd'}

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wei_Y

更这么快！听说用xx系列会吸引很多人。

戴宇轩

wei_Y 发表于 2015-3-19 17:23
更这么快！听说用xx系列会吸引很多人。

什么意思???

wei_Y

戴宇轩 发表于 2015-3-19 17:26
什么意思???

Python编程技巧系列之2---18个常用技巧。类似的。我没试过，从网上看到的。。

f2st

收藏了

stargazeryin

好吧，初学者表示完全看不懂……

xiao1yu

以后应该能用到，谢谢！

womalel

GOOD

liangbo

好东西

liangbo

学习学习

wen-wendy

以后应该用的到，先mark啦

小小新人

学习学习

June_SR

学习学习~

tiandiweicheng

谢谢，学习了

screenswindow

这么好的东西为毛不置顶？

bbxuexi

收藏

lengyudu

占个地，学习一下

comeonhcl

收获不小

蛋炒饭妖妖

虽然新人表示看不太懂。
不过感觉很有用的样子~~~

先留好标记，免得后面找不到~~~