python学习笔记。
基础知识
单例模式的4种实现
- 使用__new__方法 ```py class Singleton(object): def new(cls, *args, **kw): if not hasattr(cls, ‘_instance’): orig = super(Singleton, cls) cls._instance = orig.new(cls, *args, **kw) return cls._instance
class MyClass(Singleton): a = 1
- 共享属性
创建实例时把所有实例的__dict__指向同一个字典,这样它们具有相同的属性和方法.
```py
class Borg(object):
_state = {}
def __new__(cls, *args, **kw):
ob = super(Borg, cls).__new__(cls, *args, **kw)
ob.__dict__ = cls._state
return ob
class MyClass2(Borg):
a = 1
- 装饰器版本 ```py def singleton(cls): instances = {} def getinstance(args, **kw): if cls not in instances: instances[cls] = cls(args, **kw) return instances[cls] return getinstance
@singleton class MyClass: …
- import方法
作为python的模块是天然的单例模式
```py
# mysingleton.py
class My_Singleton(object):
def foo(self):
pass
my_singleton = My_Singleton()
# to use
from mysingleton import my_singleton
my_singleton.foo()
Python里的拷贝
引用和copy(),deepcopy()的区别
import copy
a = [1, 2, 3, 4, ['a', 'b']] #原始对象
b = a #赋值，传对象的引用
c = copy.copy(a) #对象拷贝，浅拷贝
d = copy.deepcopy(a) #对象拷贝，深拷贝
a.append(5) #修改对象a
a[4].append('c') #修改对象a中的['a', 'b']数组对象
print 'a = ', a
print 'b = ', b
print 'c = ', c
print 'd = ', d
输出结果：
a = [1, 2, 3, 4, ['a', 'b', 'c'], 5]
b = [1, 2, 3, 4, ['a', 'b', 'c'], 5]
c = [1, 2, 3, 4, ['a', 'b', 'c']]
d = [1, 2, 3, 4, ['a', 'b']]
Python的is
is是对比地址，==是对比值。
python有序字典
import collections
# 通过OrderedDict类创建的字典是有序的
dic = collections.OrderedDict()
遍历list同时输出index
for index, val in enumerate(list):
pass
数字转换成字符串，前面补0
for conIndex in range(conNum):
strIndex = str(conIndex).zfill(3) # 1 -> 001
list class 多个关键字 排序
from operator import itemgetter, attrgetter
# 对netHost.ethernetList进行排序
class IpAddr:
def __init__(self):
self.Ip = ''
self.LinkType = ''
self.Port = ''
class Ethernet:
def __init__(self):
self.linkType = ''
self.netType = ''
self.AorB = ''
self.ipAddrList = [] # the list of IpAddr
class NetHost:
def __init__(self):
self.name = ''
self.hostType = ''
self.ethernetList = [] # the list of Ethernet
print('\n---before sort---\n')
for tmpEthernet in netHost.ethernetList:
print (tmpEthernet.linkType, tmpEthernet.AorB)
netHost.ethernetList.sort(key=attrgetter('linkType', 'AorB'))
print('\n---after sort---\n')
for tmpEthernet in netHost.ethernetList:
print (tmpEthernet.linkType, tmpEthernet.AorB)
有趣的代码实现
- 打印 I LOVE U
y = 2.5
while y >= -1.6:
x = -3
while x <= 4.8:
b1 = (x*x + y*y - 1)*(x*x + y*y - 1)*(x*x + y*y - 1) <= 3.6*x*x*y*y*y
b2 = x>-2.4 and x <-2.1 and y<1.5 and y>-1
b3 = ((x<2.5 and x>2.2) or (x>3.4 and x<3.7)) and y>-1 and y<1.5
b4 = y>-1 and y<-0.6 and x<3.7 and x>2.2
if b1 or b2 or b3 or b4:
print('*',end='')
else:
print(' ',end='')
x = x+0.1
y = y-0.2
print('');
C:\>python test.py
*** ***** ***** *** ***
*** ********** ********** *** ***
*** ************* ************* *** ***
*** *************************** *** ***
*** *************************** *** ***
*** ************************* *** ***
*** *********************** *** ***
*** ********************* *** ***
*** ******************* *** ***
*** *************** *** ***
*** *********** *** ***
*** ***** ***************
*** * ***************