1. What is a variable
A variable is the amount of change
Change: the state is always changing
Quantity: to express a state
2. How to define variables
variable name=value
1) The variable name is used to find the variable value
2) Assignment symbol (=)
3) value data, used to represent a certain state
3. Garbage collection mechanism:
The Python interpreter periodically recycles values with a reference count of zero
Clear the reference count:
age=19
del age #The reference count is 0 at this time
increment reference count
age=19
age1=age #At this time, the reference count of 19 is 2
4. Each variable defined has three characteristics: id type value
id : memory address
type：int float等
value
age=19 print(id(age),type(age),age) 497538384 <class 'int'> 19
5. == and is
== Determines whether the values are equal
is to determine whether the ids are equal
6. Variable naming convention
1) The variable name must reflect the state represented by the variable value
2) The variable name can only be any combination of letters, numbers or underscores
3) The first character of the variable name cannot be a number
4) Keywords cannot be declared as variable names
['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']
7. Definition:
hump
AgeOfLichunke=19 #One high and one low, it is not recommended to define variables in this way
underscore
age_of_lichunke=19 #This method is recommended
Bad way:
1) The variable name is Chinese
2) The variable name is too long
3) Variable nouns are unsatisfactory
8. Constant: constant quantity
Constants are not defined syntactically in Python
The convention is to define constants in all uppercase: AGE_OF_LI=19