Python常用30个小技巧分享

淡淡的烟草味﹌ 2024-03-31 09:13 62阅读 0赞

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)  
8

## 找abc中最小的数 ##

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))  
0

## 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(threading)  
print(socket)  
<module ‘threading’ from ‘d:\\python351\\lib\\threading.py’>  
<module ‘socket’ from ‘d:\\python351\\lib\\socket.py’>  
7、交互环境下的“\_”操作符

在python控制台，不论我们测试一个表达式还是调用一个方法，结果都会分配给一个临时变量“\_”

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

用pdb模块设置断点

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 m1 or m2 or m3 or m4:  
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

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)  
print(shapes.quadrangle)  
0

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

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)  
6

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())

1000

1200

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))

1016

888

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)

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”)))  
True

True

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”))  
None

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