Python小技巧

1. 交换变量

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

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2. 计算技巧

    # 2的5次方
    print 2**5
    >>>32
   

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3. 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
   

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4. 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
   

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5. 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)
   

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   用下面方法写：

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

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6. 将列表转换成字符串

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

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7. 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(方法1)
   print x[-3:]
   >>> [4,5,6]
   #最后3个(方法2)
   print x[3:7]
   >>> [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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8. 集合

   用到Counter库

   from collections import Counter
   print Counter("hello")
   >>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})
   

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9. 迭代工具

   和collections库一样，还有一个库叫itertools

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

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10. 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]
    

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原文:大专栏  Python小技巧