转载:https://www.pythontab.com/html/2018/pythonjichu_0917/1351.html
编程中用到可以简化代码的30个小技巧,当然python的技巧远不止这些,让我们在学习的途中去发现宝藏吧。
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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
链状比较操作符
n = 10
print(1 < n < 20)
print(1 > n <= 9)
True
False
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
0
1
3
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]
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
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
import threading
import socket
print(threading)
print(socket)
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“_”
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}
调试脚本
用pdb模块设置断点
import pdb
pdb.ste_trace()
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
```
```
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']
```
# 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:
```
```
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)]
```
test = ["I", "Like", "Python"]
print(test)
print("".join(test))
```
['I', 'Like', 'Python']
ILikePython
```
test = [10, 20, 30]
for i, value in enumerate(test):
print(i, ':', value)
```
0 : 10
1 : 20
2 : 30
```
class shapes:
circle, square, triangle, quadrangle = range(4)
print(shapes.circle)
print(shapes.square)
print(shapes.triangle)
print(shapes.quadrangle)
```
0
1
2
3
```
def x():
return 1, 2, 3, 4
a, b, c, d = x()
print(a, b, c, d)
```
1 2 3 4
```
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
```
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
```
import functools
result = (lambda k: functools.reduce(int.__mul__, range(1, k+1), 1))(3)
print(result)
```
6
```
test = [1, 2, 3, 4, 2, 2, 3, 1, 4, 4, 4, 4]
print(max(set(test), key=test.count))
```
4
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
```
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
```
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
```
import sys
lprint = lambda *args: sys.stdout.write(" ".join(map(str, args)))
lprint("python", "tips", 1000, 1001)
```
python tips 1000 1001
```
t1 = (1, 2, 3)
t2 = (10, 20, 30)
print(dict(zip(t1, t2)))
```
{1: 10, 2: 20, 3: 30}
```
print("http://localhost:8888/notebooks/Untitled6.ipynb".startswith(("http://", "https://")))
print("http://localhost:8888/notebooks/Untitled6.ipynb".endswith((".ipynb", ".py")))
```
True
True
```
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]
```
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
5
拼接字符串的7种方法
s = 'Hello'+' '+'World'+'!'
print(s)
strlist=['Hello',' ','World','!']
print(''.join(strlist))
s='{} {}!'.format('Hello','World')
print(s)
s = '%s %s!' % ('Hello', 'World')
print(s)
s = (
'Hello'
' '
'World'
'!'
)
print(s)
from string import Template
s = Template('${s1} ${s2}!')
print(s.safe_substitute(s1='Hello',s2='World'))
输出结果:Hello World!
Template的实现方式是首先通过Template初始化一个字符串。这些字符串中包含了一个个key。通过调用substitute或safe_subsititute,将key值与方法中传递过来的参数对应上,从而实现在指定的位置导入字符串。这种方式的好处是不需要担心参数不一致引发异常,如:
from string import Template
s = Template('${s1} ${s2} ${s3}!')
print(s.safe_substitute(s1='Hello',s2='World'))
输出结果:Hello World ${s3}!
通过F-strings拼接
在python3.6.2版本中,PEP 498 提出一种新型字符串格式化机制,被称为“字符串插值”或者更常见的一种称呼是F-strings,F-strings提供了一种明确且方便的方式将python表达式嵌入到字符串中来进行格式化:
s1='Hello'
s2='World'
print(f'{s1} {s2}!')
输出结果:Hello World!
在F-strings中我们也可以执行函数:
def power(x):
return x*x
x=4
print(f'{x} * {x} = {power(x)}')
输出结果:4 * 4 = 16
而且F-strings的运行速度很快,比%-string和str.format()这两种格式化方法都快得多。