# Python初学者的17个技巧

### 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

``````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

``````numbers = [1,2,3,4,5,6]
even = []
for number in numbers:
if number%2 == 0:
even.append(number)
``````

``````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

``````data = {'user': 1, 'name': 'Max', 'three': 4}
try:
except KeyError:
``````

``````data = {'user': 1, 'name': 'Max', 'three': 4}
``````

### 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]
#偶数项
print x[1::2]
>>> [2,4,6]
``````

### 60个字符解决FizzBuzz

``````写一个程序，打印数字1到100，3的倍数打印“Fizz”来替换这个数，5的倍数打印“Buzz”，对于既是3的倍数又是5的倍数的数字打印“FizzBuzz”。
``````

``````for x in range(101):print"fizz"[x%3*4::]+"buzz"[x%5*4::]or x
``````

### 集合

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

### 迭代工具

``````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')
``````

### False == True

``````False = True
if False:
print "Hello"
else:
print "World"
>>> Hello
``````

##### 不写代码的码农

Front-end Dev Handbook: 前端开发者手册

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