30个python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, 20
print(x, y)
y, x = x, y
print(x, y)

 

10 20
20 10

 

2、链状比较操作符

In [3]:

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]

In [4]:

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

 

0
1
3
3

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 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

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 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

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 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

In [12]:

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

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)

 

5
3
1

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 : 10
1 : 20
2 : 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)

 

0
1
2
3

 

18、从方法中返回多个值

In [28]:

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

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 y
1 2 3
10 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))

 

12
6

 

21、计算任何数的阶乘

In [38]:

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

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 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

In [42]:

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

In [47]:

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

In [49]:

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

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")))

 

True
True

 

29、不使用循环构造一个列表

In [55]:

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

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"))

 

None
2