python的30个编程技巧

从公众号上看到了一篇文章《30个python编程技巧！》，觉得有些挺有用的，有的也一直在用，就挨个实现了一下。

   1、原地交换两个数字

In [1]:

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

10 2020 10

2、链状比较操作符

In [3]:

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

TrueFalse

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]

In [4]:

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

8

In [6]:

# 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))

0133

In [7]:

# 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

In [15]:

multistr = "select * from multi_row \where row_id < 5"print(multistr)

select * from multi_row where row_id < 5

In [16]:

multistr = """select * from multi_row where row_id < 5"""print(multistr)

select * from multi_row where row_id < 5

In [17]:

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

In [18]:

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

In [19]:

import threadingimport socketprint(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

In [1]:

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

In [ ]:

import pdbpdb.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

In [ ]:

python -m http.server

11、检查python中的对象

In [3]:

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']

In [4]:

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

In [ ]:

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

13、运行时检测python版本

In [12]:

import sysif 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 2.7current 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

In [19]:

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

In [21]:

# 翻转列表本身testList = [1, 3, 5]testList.reverse()print(testList)

[5, 3, 1]

In [23]:

# 在一个循环中翻转并迭代输出for element in reversed([1, 3, 5]):    print(element)

531

In [24]:

# 翻转字符串print("Test Python"[::-1])

nohtyP tseT

In [25]:

# 用切片翻转列表print([1, 3, 5][::-1])

[5, 3, 1]

16、用枚举在循环中找到索引

In [26]:

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

0 : 101 : 202 : 30

17、定义枚举量

In [27]:

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

0123

18、从方法中返回多个值

In [28]:

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

1 2 3 4

19、使用*运算符unpack函数参数

In [35]:

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 y1 2 310 20 30

20、用字典来存储表达式

In [37]:

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

126

21、计算任何数的阶乘

In [38]:

import functoolsresult = (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

In [40]:

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

In [41]:

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

10001200

24、检查一个对象的内存使用

In [42]:

import sysx = 1print(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

In [47]:

import sys# 原始类class FileSystem(object):    def __init__(self, files, folders, devices):        self.files = files        self.folder = folders        self.devices = devicesprint(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 = devicesprint(sys.getsizeof(FileSystem))

1016888

26、用lambda 来模仿输出方法

In [49]:

import syslprint = 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

In [50]:

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

In [52]:

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

TrueTrue

29、不使用循环构造一个列表

In [55]:

import itertoolsimport numpy as nptest = [[-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

In [58]:

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"))

None2