variable
What is variable
All things described changes state
Compositional variables
Variable name (variable value received) = (assignment symbol) variable value (value)
Naming the variable name
weight = 160
name = 'hyc'
Variable names must consist of number / letter / underscore _ Composition
stu_name = 'hyc'
Variable names are readable (sense) deposit is not an end, is the purpose of taking
Do not arbitrarily take a variable name, such as meaningless _ like
Do not use keywords
Do not use as variable names such as print, if, as and the like
Two kinds of ways defined variable names
Underline style
(General use, the convention)
stu_name = 'hyc'
Hump body
StuName = 'hyc'
Variable Memory Management
Define the variable
print (180) # print will automatically help you create a variable 180, after printing, immediately release the memory space 180
Define a variable, it opens up the memory space to store a memory variable
Reference count
height = 180 # 180 reference count plus 1
x = height # reference count plus 1
reference count by del x # 1
del height # reference count is 0
When the reference count is 0, triggering garbage collection mechanism to release the memory occupied
[-5,256] when the python interpreter starts automatically opened up, so the impact of garbage collection will not be affected
pycharm If the time interval is short, no matter what value are the same id
Three variables defined feature
Get the memory address of the variable value for the variable values
print(id(stu_name))
Get variable data types for variable values
print（type(stu_name)）
Print variable values
print(stu_name)
constant
The same amount, the constant nature is also a variable
All the letters are capitalized constants
After working in all capital letters is a constant quantity, do not go changing
AGE = 1
Note
So that when the code is not to be construed in python interpreter to run, that let him senseless
Note wherein the code block in the above code, the remaining single annotation (such as variable names) on the back code
Single-line comments
Comment on the statement by the former #
Multi-line comments
With '' '' '' on the need to comment out multiple lines of statements
Fancy assignment
Cross assignment
height_of_teacher, height_of_stu = 170,170
Modify x and y in the case to ensure that the same memory address
Create a new variable z, x and y to be interchangeable by the assignment of z
z = x
x = y
y = z
Cross assignment
x, y = y, x
The same memory address, the same value necessarily the same value, not necessarily the same memory address
Chain assignment
a = b = c = 10
uncommonly used