Day2

变量的创建过程

name = "qiangzi"
>>> id(name)
19194464  #内存地址id
>>>

......

>>> name = "qiangzi"

>>> id(name)
19194464
>>> name = "daqiang"
>>> id(name)
19196576

python解释器有自动垃圾回收机制，自动隔一段时间把没有跟变量名关联的内存数回收。

变量指向关系

>>> name = "qiangzi"
>>> name1 = name
>>> id(name),id(name1)
(29483616, 29483616)

.....

>>> name = "qiangzi"
>>> name1 = name
>>> name = "强子"
>>> id(name),id(name1)
(25097712, 25092704)
>>> name,name1
('强子', 'qiangzi')

身份运算和None

>>> name = "qiangzi"
>>> age = 25
>>> name,age
('qiangzi', 25)
>>> type(name),type(age)
(<class 'str'>, <class 'int'>)

# class类别  str字符串   int整数

is    is是判断两个标识符是不是引用自一个对象，如果引用一个一个对象则返回True，否则返回False

is not   is not是判断两个标识符是不是引用自不同对象，如果引用不是同一对象则返回True，否则返回False。

>>> name = "qiangzi"
>>> age = 25
>>> name,age
('qiangzi', 25)
>>> type(name),type(age)
(<class 'str'>, <class 'int'>)

>>> type(name) is str
True
>>> type(age) is not int
False

None   空  Empty

三元运算

>>> a = 10

>>> b = 8

>>> if a > 15:

... c = a
... else:
... c = b

>>> print(c)

8

简化   c = 值1 if 条件A else 条件B

如果条件A成立，就去左边的 值1，则取 值2

>>> a = 10
>>> b = 8
>>> c = a if a > 15 else b
>>> c
8