Python中国社区  »  python开源

爬虫工程师不得不知道的30个Python常用小技巧

也随风落 • 4 天前 • 32 次点击  

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

最后: 怎么样才能学好python

0基础入门python http://www.makeru.com.cn/course/details/1804.html?s=70408

学好python你需要一个良好的环境,一个优质的开发交流群,群里都是那种相互帮助的人才是可以的,我有建立一个python学习交流群,在群里我们相互帮助,相互关心,相互分享内容,这样出问题帮助你的人就比较多,群号是577040823,这样就可以找到大神聚合的群,如果你只愿意别人帮助你,不愿意分享或者帮助别人,那就请不要加了,你把你会的告诉别人这是一种分享。

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 1 3 3 1 2 3

列表推导

x = [m2 if m>10 else m4 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 1 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'] 1 2 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) print(shapes.quadrangle) 0 1 2 3

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") print(stdcalc"subtract") 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) 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

28

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

Python社区是高质量的Python/Django开发社区
本文地址:http://www.python88.com/topic/31618
 
32 次点击  
分享到微博