python要点

a = ‘abc‘       #内存创建变量a, 字符串‘abc‘
b = a           #创建变量b， b指向a地址，也就是‘abc‘
a = ‘xyz‘       #创建字符串‘xyz‘，a指向‘xyz’
print b         #b指针没变，所以还是‘abc’

a = {}          #创建变量a,创建对象{}，a指向{}
b  = a          #创建变量b， b指向a地址，也就是{}
a[‘a1‘] = 1     #修改a指向内容的数据
print b==a,b    #b指针没变，所以内容跟a看到的一样
a = {}          #重新创建对象{}，a指向它，跟前一个不一样
a[‘a2‘] = 2     #修改新对象属性
print b==a,a,b  #b还为原先的值，{‘a1‘:1},所以深拷贝可由此实现

# coding=utf-8
#浅拷贝
a = [1,2,3,4,5]
b = a
a.append(‘hello‘)
print a == b, a, b

#深拷贝
from copy import copy
c = copy(a)
a.append(‘world‘)
print a == c, a, c

#输出结果
True [1, 2, 3, 4, 5, ‘hello‘] [1, 2, 3, 4, 5, ‘hello‘]
False [1, 2, 3, 4, 5, ‘hello‘, ‘world‘] [1, 2, 3, 4, 5, ‘hello‘]

# coding=utf-8
a = abs         #变量abs指向绝对值函数，a指向abs指向的地址
print a(-1)
abs = 3         #变量abs指向整数对象3 
print a(-1)
print abs(-1)   #再调就会报错，因为他已经不是绝对值函数了

def test1():
    return 1,2
def test2():
    return (1,2)
def test3():
    return [1,2]
a, b = test1()
print a, b, type(test1())
a, b = test2()
print a, b, type(test2())
a, b = test3()
print a, b, type(test3())

#输出
1 2 <type ‘tuple‘>
1 2 <type ‘tuple‘>
1 2 <type ‘list‘>

def m_power(x, n=2):
    s = 1
    while(n>0):
        s*=x
        n-=1
    return s
print m_power(10)
print m_power(10,3)
print m_power(10,n=3)

#输出
100
1000
1000

#可变参数函数手动实现
def test(nums):
    sum = 0
    for n in nums:
        sum += n
    return sum
print test([1,2,3,4,5])

#可变参数
def test(*nums):#为什么此处重名没报错？？？
    sum = 0
    for n in nums:
        sum += n
    return sum
print test(1,2,3,4,5)
nums = [1,2,3,4,5]
print test(*nums)

#输出
15
15
15

#关键字参数手动实现
from copy import copy
def test2(props):
    temp = copy(props)
    temp[‘test_2‘] = 2
    return temp
kw = {‘a‘:1,‘b‘:2}
print test2(kw)

#关键字参数
def test3(**props):
    props[‘test_3‘] = 2
    return props
print test3(**kw)
print test3(a=1,b=2)

#输出
{‘a‘: 1, ‘b‘: 2, ‘test_2‘: 2}
{‘a‘: 1, ‘b‘: 2, ‘test_3‘: 2}
{‘a‘: 1, ‘b‘: 2, ‘test_3‘: 2}