Python初学者的17个技巧

骑猪看日落 2022-08-08 09:17 324阅读 0赞

### 交换变量 ###

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

### if 语句在行内 ###

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

### 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酷。

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

### 计算技巧 ###

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

### 注意浮点数的除法 ###

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

### 数值比较 ###

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

### 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

### 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

### 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)

用下面的代替

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

### 字典推导 ###

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

### 初始化列表的值 ###

items = [0]*3
    print items
    >>> [0,0,0]

### 将列表转换成字符串 ###

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

### 从字典中获取元素 ###

不要用下列的方式

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

替换为

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

### 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
    print x[-3:]
    >>> [4,5,6]
    #奇数项
    print x[::2]
    >>> [1,3,5]

译文出处：[Python初学者的17个技巧][Python_17]

[Python_17]: http://www.ido321.com/1550.html