# 最值得你收藏的30个Python常用小技巧

1、原地交换两个数字

``````x, y =10, 20
print(x, y)
y, x = x, y
print(x, y)
``````

10 20

20 10

2、链状比较操作符

``````n = 10
print(1 < n < 20)
print(1 > n <= 9)
``````

True

False

3、使用三元操作符来实现条件赋值

[表达式为真的返回值] if [表达式] else [表达式为假的返回值]

``````y = 20
x = 9 if (y == 10) else 8
print(x)
``````

``````def small(a, b, c):
return a if a<b and a<c else (b if b<a and b<c else c)
print(small(1, 0, 1))
print(small(1, 2, 2))
print(small(2, 2, 3))
print(small(5, 4, 3))

``````
``````# 列表推导
x = [m**2 if m>10 else m**4 for m in range(50)]
print(x)
``````

[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561, 10000, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849, 1936, 2025, 2116, 2209, 2304, 2401]

4、多行字符串

``````multistr = "select * from multi_row \
where row_id < 5"
print(multistr)
select * from multi_row where row_id < 5
multistr = """select * from multi_row
where row_id < 5"""
print(multistr)
select * from multi_row
where row_id < 5
multistr = ("select * from multi_row"
"where row_id < 5"
"order by age")
print(multistr)
select * from multi_rowwhere row_id < 5order by age

``````

5、存储列表元素到新的变量

``````testList = [1, 2, 3]
x, y, z = testList    # 变量个数应该和列表长度严格一致
print(x, y, z)
``````

1 2 3

6、打印引入模块的绝对路径

``````import threading
import socket
print(socket)
<module 'socket' from 'd:\\python351\\lib\\socket.py'>
``````

7、交互环境下的“_”操作符

8、字典/集合推导

``````testDic = {i: i * i for i in range(10)}
testSet = {i * 2 for i in range(10)}
print(testDic)
print(testSet)
``````

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}

{0, 2, 4, 6, 8, 10, 12, 14, 16, 18}

9、调试脚本

``````import pdb
pdb.ste_trace()
``````

10、开启文件分享

python允许开启一个HTTP服务器从根目录共享文件

``````python -m http.server
``````

11、检查python中的对象

``````test = [1, 3, 5, 7]
print(dir(test))
``````

[‘add’, ‘class’, ‘contains’, ‘delattr’, ‘delitem’, ‘dir’, ‘doc’, ‘eq’, ‘format’, ‘ge’, ‘getattribute’, ‘getitem’, ‘gt’, ‘hash’, ‘iadd’, ‘imul’, ‘init’, ‘iter’, ‘le’, ‘len’, ‘lt’, ‘mul’, ‘ne’, ‘new’, ‘reduce’, ‘reduce_ex’, ‘repr’, ‘reversed’, ‘rmul’, ‘setattr’, ‘setitem’, ‘sizeof’, ‘str’, ‘subclasshook’, ‘append’, ‘clear’, ‘copy’, ‘count’, ‘extend’, ‘index’, ‘insert’, ‘pop’, ‘remove’, ‘reverse’, ‘sort’]

``````test = range(10)
print(dir(test))
``````

[‘class’, ‘contains’, ‘delattr’, ‘dir’, ‘doc’, ‘eq’, ‘format’, ‘ge’, ‘getattribute’, ‘getitem’, ‘gt’, ‘hash’, ‘init’, ‘iter’, ‘le’, ‘len’, ‘lt’, ‘ne’, ‘new’, ‘reduce’, ‘reduce_ex’, ‘repr’, ‘reversed’, ‘setattr’, ‘sizeof’, ‘str’, ‘subclasshook’, ‘count’, ‘index’, ‘start’, ‘step’, ‘stop’]

12、简化if语句

``````# use following way to verify multi values
if m in [1, 2, 3, 4]:
# do not use following way
if m==1 or m==2 or m==3 or m==4:
``````

13、运行时检测python版本

``````import sys
if not hasattr(sys, "hexversion") or sys.version_info != (2, 7):
print("sorry, you are not running on python 2.7")
print("current python version:", sys.version)
``````

sorry, you are not running on python 2.7

current python version: 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25) [MSC v.1900 64 bit (AMD64)]

14、组合多个字符串

``````test = ["I", "Like", "Python"]
print(test)
print("".join(test))
``````

[‘I’, ‘Like’, ‘Python’]

ILikePython

15、四种翻转字符串、列表的方式

5

3

1

16、用枚举在循环中找到索引

``````test = [10, 20, 30]
for i, value in enumerate(test):
print(i, ':', value)
``````

0 : 10

1 : 20

2 : 30

17、定义枚举量

``````class shapes:
circle, square, triangle, quadrangle = range(4)
print(shapes.circle)
print(shapes.square)
print(shapes.triangle)
``````

18、从方法中返回多个值

``````def x():
return 1, 2, 3, 4
a, b, c, d = x()
print(a, b, c, d)
``````

1 2 3 4

19、使用*运算符unpack函数参数

``````def test(x, y, z):
print(x, y, z)
testDic = {'x':1, 'y':2, 'z':3}
testList = [10, 20, 30]
test(*testDic)
test(**testDic)
test(*testList)
``````

z x y

1 2 3

10 20 30

20、用字典来存储表达式

``````stdcalc = {
"sum": lambda x, y: x + y,
"subtract": lambda x, y: x - y
}
print(stdcalc["sum"](9, 3))
print(stdcalc["subtract"](9, 3))
``````

12

6

21、计算任何数的阶乘

``````import functools
result = (lambda k: functools.reduce(int.__mul__, range(1, k+1), 1))(3)
print(result)
``````

22、找到列表中出现次数最多的数

``````test = [1, 2, 3, 4, 2, 2, 3, 1, 4, 4, 4, 4]
print(max(set(test), key=test.count))
4
``````

23、重置递归限制

python限制递归次数到1000，可以用下面方法重置

``````import sys
x = 1200
print(sys.getrecursionlimit())
sys.setrecursionlimit(x)
print(sys.getrecursionlimit())

``````

24、检查一个对象的内存使用

``````import sys
x = 1
print(sys.getsizeof(x))    # python3.5中一个32比特的整数占用28字节
``````

25、使用slots减少内存开支

``````import sys
# 原始类
class FileSystem(object):
def __init__(self, files, folders, devices):
self.files = files
self.folder = folders
self.devices = devices
print(sys.getsizeof(FileSystem))
# 减少内存后
class FileSystem(object):
__slots__ = ['files', 'folders', 'devices']
def __init__(self, files, folders, devices):
self.files = files
self.folder = folders
self.devices = devices
print(sys.getsizeof(FileSystem))
``````

26、用lambda 来模仿输出方法

``````import sys
lprint = lambda *args: sys.stdout.write(" ".join(map(str, args)))
lprint("python", "tips", 1000, 1001)
``````

27、从两个相关序列构建一个字典

``````t1 = (1, 2, 3)
t2 = (10, 20, 30)
print(dict(zip(t1, t2)))
``````

{1: 10, 2: 20, 3: 30}

28、搜索字符串的多个前后缀

``````print("http://localhost:8888/notebooks/Untitled6.ipynb".startswith(("http://", "https://")))
print("http://localhost:8888/notebooks/Untitled6.ipynb".endswith((".ipynb", ".py")))
``````

29、不使用循环构造一个列表

``````import itertools
import numpy as np
test = [[-1, -2], [30, 40], [25, 35]]
print(list(itertools.chain.from_iterable(test)))
``````

[-1, -2, 30, 40, 25, 35]

30、实现switch-case语句

``````def xswitch(x):
return  xswitch._system_dict.get(x, None)
xswitch._system_dict = {"files":10, "folders":5, "devices":2}
print(xswitch("default"))
print(xswitch("devices"))
``````

JavaScript常用特效chm下载

2015-11-12
css布局的各种FC简单介绍：BFC，IFC，GFC，FFC

2018-05-17

&lt;font face=&quot;寰�杞�闆呴粦, Arial, sans-serif &quot;&gt;2014骞达紝杞�浠惰�屼笟鍙戝睍杩呴€燂紝鍚勭�嶈��瑷€灞傚嚭涓嶇┓锛屼互婊¤冻鐢ㄦ埛涓嶆柇鍙樺寲鐨勯渶姹傘€傝繖浜涜��...
2015-11-12
12个你未必知道的CSS小知识

2015-11-12
ajax为什么令人惊异？ajax的优缺点

2015-11-12
HTML5的5个不错的开发工具推荐
HTML5规范终于在今年正式定稿，对于从事多年HTML5开发的人员来说绝对是一个重大新闻。数字天堂董事长，DCloud CEO王安也发表了文章，从开发者和用户两个角度分析了HTML对两个人群的优势。其实，关于HTML5的开发工具，我们以往的...
2015-11-12
JavaScript教程：JS中的原型
Keith Peters 几年前发表的一篇博文，关于学习没有“new”的世界，其中解释了使用原型继承代替构造函数。两者都是纯粹的原型编码。 标准方法（The Standard Way） 一直以来，我们学习的在 JavaScript 里创建对...
2015-11-12
AJAX的浏览器支持
AJAX 的要点是 XMLHttpRequest 对象。 不同的浏览器创建 XMLHttpRequest 对象的方法是有差异的。 IE 浏览器使用 ActiveXObject，而其他的浏览器使用名为 XMLHttpRequest 的 Jav...
2015-11-12
JavaScript的组成

2015-11-12
2014年最流行前端开发框架对比评测

2015-11-12