day 7 引用

1.b=a在c语言和python中的区别

c语言：a=100 a变量里面放的100

b = a b变量里面也放的100

python ： a=100 内存中有个100 a放的100的内存地址

　　　　 b = a b也放的100的内存地址

　　相当于给100那一块内存，贴个便利签

2.type查看数据类型，id查看内存地址

　　注意：自动垃圾回收机制！！多余的内存会回收

3.可变类型列表，字典

不可变类型数字字符串元组

####  字符串
In [1]: a = "hello"In [2]: a = "world"In [3]: In [3]: a[0]
Out[3]: 'w'In [4]: a[0]= "W"
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-30f9d655f9db> in <module>()
----> 1 a[0]= "W"TypeError: 'str' object does not support item assignment

#####  元组
In [5]: b = (1,2,3)In [6]: b[0]
Out[6]: 1In [7]: b[0] = 111
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-7-3184fba1d024> in <module>()
----> 1 b[0] = 111TypeError: 'tuple' object does not support item assignment

##### 可变类型  list列表  dict字典
In [8]: a = [11,22,33]In [9]: a[0] = 'fff'In [10]: a
Out[10]: ['fff', 22, 33]

###  不可变类型都可以当做 字典的key
In [11]: a = {"name":"alex",3.14:"jack"}In [12]: a = {"name":"alex",3.14:"jack",(1,2,3):"tom"}In [13]: a = {"name":"alex",3.14:"jack",(1,2,3):"tom",[11,22]:"fjfj"}
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-13-6fdc428d8d83> in <module>()
----> 1 a = {"name":"alex",3.14:"jack",(1,2,3):"tom",[11,22]:"fjfj"}TypeError: unhashable type: 'list'