A variable is Python The storage unit used by the program to store the calculation results , For easy access to this storage unit ,Python Name this storage unit , This name is the variable name , stay Python Access the storage unit that holds the calculation results through the variable name in .
This official textbook interpretation is somewhat obscure , Combined with the... In our life Drink lots of water Scene to explain .
In our daily life, we will use glass Come and drink some water , But besides drinking water , We can also use the same cup to drink tea 、 Drink coke 、 Drink Maotai and so on ( I drink Maotai with a cup ).
The cup here can be seen as “ Variable ”, water 、 tea 、 Cola and so on are the values of variables , Pour water into the cup 、 pour tea 、 Pour coke for The assignment of the cup variable .
From this scene we can know , A cup of water is a variable , The cup is the variable name , And water 、 Tea is the value of the variable . Variables consist of variable names and values , The variable is constant, but the value of the variable can change .
summary ：
- A variable is the process of an assignment statement
- You can change the value of a variable by assigning a value to its name
- The variable name can remain unchanged , Variable values can be changed at any time
- A variable name with a variable value is a variable
When we name a variable , Where do variables exist ？ After all, it is invisible and untouchable , In fact, the memory of our computer is composed of many memory blocks . Every time we declare a variable , Will be stored in our memory . Of course , Variables are not stored indefinitely in memory , After all, our memory is limited , So when many variables are stored in our memory , There will be insufficient memory space .
summary ：
- Variables exist in the memory of our computer , The computer's memory is divided into many memory blocks
- After each variable is defined, it is stored in a memory block , If there are too many variables , Memory may be out of space
The picture below is Python Diagram of variables and memory in
- form ： It has to be numbers 、 Letter 、 Underline _ form
- requirement ： The beginning must be non numeric , Do not use special symbols , for example ：
!、@、#、$、%etc.- Be careful ： Case sensitive , The name should be meaningful , Hump nomenclature or underline nomenclature
- length ： Although it is of any length , But not too long , Poor readability
- a key ： It can't be Python Keywords already exist , If you use keywords, the original keyword function will be lost , This is not recommended
- chinese ： stay python2 Chinese cannot be used as the variable name in ; stay python3 Chinese variable names can be used , However, it is not recommended to use in the development environment
Legal variable names are as follows ：
- name
- SEX
- creat_table
- _drop_user
- select__mobile, The name contains 2 Root underline
- _init_, The name contains 2 Root underline
- OpenLesson, Although this hump type variable name can be used in Python Use in , But it's not a standard method , So it's not recommended
Illegal variable names are as follows ：
- get t a b l e , The life name package contain 了 word operator table, The name contains the characters table, The life name package contain 了 word operator
- ab/c, The name contains the characters / And it doesn't make any sense
- 01class_name, The number cannot start with a variable name
Now let's do a little exercise on variable names
name = "Neo"
birthday = "2000-01-01"
cat_name, cat_years = "mimi", "3" # Multiple variable names , It can be used continuously , But the left and right numbers must be the same
if __name__ == '__main__':
print("my name is：" + name)
print("my birthday is：" + birthday)
print("I have a cat,name is：" + cat_name, "years is：" + cat_years)
The operation results are as follows ：
It should be noted that the explicit specifications of different programming languages are also different ~
Python General principles for naming recommendations ：
- Modules should be named in lowercase as much as possible , Keep the initials in lowercase , Try not to underline
- Class names use humps (CamelCase) Naming style , title case , Private classes can start with an underscore
- All function names are lowercase , If there are more than one word , Separate... With underscores
- Private functions can start with an underline
- Try to lower the variable name , If there are more than one word , Separate... With underscores
- Constants are in uppercase , If there are more than one word , Use an underline to separate
python Internal special words for processing business logic , We mentioned above , Variable names should never be named by keywords ！
What is the difference between variable names and keywords ？
Variable names are used to assign values to variables ; Keyword is used for business logic processing .
Actually in python There is no keyword classification in . But if we use some keywords as variable names , Will report an error directly , This kind of keyword can be called Strong keyword ;
On the contrary, when we use some keywords as variable names , No errors are reported , But it will lose the original function of keywords , This kind of keyword can be called Weak keyword , It's usually python Built in functions in .
python Common keywords in , The keywords in the following table are Strongly typed keywords Never use it as a variable
Let's try to use Strong keyword As a variable name
False yes Python Key words of , So the prompt syntax error ：SyntaxError: can’t assign to keyword.
Try again Weak keyword As a variable name
