Python初學者的17個技巧

英文原文：http://www.maxburstein.com/blog/python-shortcuts-for-the-python-beginner/

交換變量

x = 6
y = 5

x, y = y, x

print x
>>> 5
print y
>>> 6

if 語句在行內

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

連接

下面的最後一種方式在綁定兩個不同類型的對象時顯得很酷。

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

計算技巧

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

注意浮點數的除法

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

數值比較

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

兩個列表同時迭代

nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
for teama, teamb in zip(nfc, afc):
     print teama + " vs. " + teamb
>>> Packers vs. Ravens
>>> 49ers vs. Patriots

帶索引的列表迭代

teams = ["Packers", "49ers", "Ravens", "Patriots"]
for index, team in enumerate(teams):
    print index, team
>>> 0 Packers
>>> 1 49ers
>>> 2 Ravens
>>> 3 Patriots

列表推導

已知一個列表，刷選出偶數列表方法：

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]

字典推導

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]

將列表轉換成字符串

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

從字典中獲取元素

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

替換爲

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

獲取子列表

x = [1,2,3,4,5,6]
#前3個
print x[:3]
>>> [1,2,3]
#中間4個
print x[1:5]
>>> [2,3,4,5]
#最後3個
print x[-3:]
>>> [4,5,6]
#奇數項
print x[::2]
>>> [1,3,5]
#偶數項
print x[1::2]
>>> [2,4,6]

60個字符解決FizzBuzz

前段時間Jeff Atwood 推廣了一個簡單的編程練習叫FizzBuzz，問題引用如下：

寫一個程序，打印數字1到100，3的倍數打印“Fizz”來替換這個數，5的倍數打印“Buzz”，對於既是3的倍數又是5的倍數的數字打印“FizzBuzz”。

這裏有一個簡短的方法解決這個問題：

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

集合

用到Counter庫

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

迭代工具

和collections庫一樣，還有一個庫叫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')

False == True

在python中，True和False是全局變量，因此：

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

譯文首發：http://blog.92fenxiang.com/articles/1421931112