[基础] 给Python初学者的一些技巧
在 Python 2.7.5 和 Python 3.3.2 中进行测试, 更正部分不一致
英文原文: Python Shortcuts for the Python Beginner —— Max Burstein, 编译: 伯乐在线 – 刘志军
译文链接：http://blog.jobbole.com/32748/
以下是我近些年收集的一些Python实用技巧和工具，希望能对你有所帮助。
交换变量 Swapping Variables
x = 6
y = 5
x, y = y, x
print(x)
>>> 5
print(y)
>>> 6
行内 if 语句 Inline if Statement
print("Hello" if True else "World")
>>> Hello
连接 Concatenations
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cool.
nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
print nfc + afc
>>> ['Packers', '49ers', 'Ravens', 'Patriots']
print str(1) + " world"
>>> 1 world
print '1' + " world" # 这里在Python3中使用单引号会出错
>>> 1 world
print 1, "world"
>>> 1 world
print nfc, 1
>>> ['Packers', '49ers'] 1
print(nfc, 1) # 注意这里与Python3不同
>>> (['Packers', '49ers'], 1)
Python3中略有不同:
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
数字技巧 Number Tricks
# 除后向下取整 Floor Division (rounds down)
print(5.0//2)
>>> 2.0
# 2的5次方
print 2**5
>> 32
注意浮点数的除法
print .3/.1
>>> 2.9999999999999996 # Python2 中输出 3.0
print(.3//.1)
>>> 2.0
数值比较 Numerical Comparison
这是我见过诸多语言中很少有的如此棒的简便法
x = 2
if 3 > x > 1:
print(x)
>>> 2
if 1 < x > 0:
print(x)
>>> 2
同时迭代两个列表 Iterate Through Two Lists at the Same Time
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 Iterate Through List With an Index
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 List Comprehension
使用列表推导我们可以将下面代码:
numbers = [1,2,3,4,5,6]
even = []
for number in numbers:
if number%2 == 0:
even.append(number)
转变成:
numbers = [1,2,3,4,5,6]
even = [number for number in numbers if number%2 == 0]
是不是很牛呢, 哈哈.
字典推导 Dictionary Comprehension
和列表推导类似, 字典可以做同样的工作：
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print({key: value for value, key in enumerate(teams)})
>>> {'49ers': 1, 'Ravens': 2, 'Patriots': 3, 'Packers': 0}
# Python3 >>> {'Packers': 0, 'Patriots': 3, 'Ravens': 2, '49ers': 1}
初始化列表的值 Initialize List Values
items = [0]*3
print(items)
>>> [0,0,0]
The [0]*3 is nice, but you have to be careful with it. You can hit a big snag with references For instance:
a = [[]]*3 # [[], [], []]
a[0].append(0) # [[0], [0], [0]]
列表转换为字符串 Converting a List to a String
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print(", ".join(teams))
>>> Packers, 49ers, Ravens, Patriots
从字典中获取元素 Get Item From Dictionary
我承认try/except代码并不雅致, 不过这里有一种简单方法, 尝试在字典中查找key, 如果没有找到对应的value将用第二个参数设为其变量值.
data = {'user': 1, 'name': 'Max', 'three': 4}
try:
is_admin = data['admin']
except KeyError:
is_admin = False
你可以这样做:
data = {'user': 1, 'name': 'Max', 'three': 4}
is_admin = data.get('admin', False)
获取列表的子集 Taking a Subset of a List
有时，你只需要列表中的部分元素，这里是一些获取列表子集的方法。
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]
#Reverse List
print(x[::-1])
>>> [6,5,4,3,2,1]
60个字符解决FizzBuzz问题 FizzBuzz in 60 Characters
前段时间 Jeff Atwood 推广了一个简单的编程练习叫FizzBuzz, 问题引用如下：
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".
这里是一个简短的, 有意思的方法解决这个问题:
for x in range(101):print("fizz"[x%3*4::]+"buzz"[x%5*4::] or x)
集合 Collections
除了python内置的数据类型外, 在collection模块同样还包括一些特别的用例. 在有些场合Counter非常实用. 如果你参加过在这一年的Facebook HackerCup, 你甚至也能找到他的实用之处.
from collections import Counter
print Counter("hello")
>>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})
迭代工具 Itertools
和collections库一样, python还有一个库叫itertools, 对某些问题真能高效地解决. 其中一个用例是查找所有组合. 它能告诉你在一个组中元素的所有不同的组合方式.
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 (Python2)
比起实用技术来说这是一个很有趣的事. 在python中, True和False是全局变量. 因此:
False = True
if False:
print "Hello"
else:
print "World"
>>> Hello
In python 2 True and False are basically just global variables. In Python 3 they are keywords.
如果你还有任何很酷的奇技淫巧, 可以在下面留言, 感谢阅读.
