python interpreter role
After writing python code is stored, we will get a .py extension to a text file. To do this, run the file you need python interpreter.
Two ways to run the python program
Interactive mode
In Python interactive environment, you can only enter Python code and execute immediately.
Command line mode
Command line mode is executed .py text files.
Note
What is a comment?
Notes that the code of explanatory notes, comments will not be content as the code runs.
Why should we comment?
Enhance the readability of the code
How to use annotations?
Single-line and multi-line comments
1. Single-line comments using a #, the code may be followed immediately above or immediately behind
2. Multi-line comments may be three pairs or three pairs of double quotes single quotes
What is IDE? Why should IDE?
That IDE integrated development environment. The best Python IDE tool is pyCharm
IDE is a function of n software can inherit, but there is code hinting and error correction function, can greatly improve development efficiency.
variable
What is a variable? Why should there be variable? How to use variables?
Variable is the amount may vary
In order to let the computer like people to remember things in a certain state, and the state changes can occur.
These three parts are variable names assigned symbol value of the variable a = 1 Example
Naming the variable name
1. Variable names can only be a combination of letters, numbers, or underscore
2. The first character variable names can not be digital
3. Keywords can not be defined as a variable
4. You can not use Chinese when the variable name (although they would succeed, but the very suggestion, too low a)
Only if it meets all the above conditions can be successfully defined variable names
Variable naming style
1. hump body
Capitalize the first letter of each word such as: Name_Age = 18
2. underscore body
Between each word, for example, underlined: Name_Age = 18
constant
What is constant? Why should there be constant? How to use constants?
Constant is the amount in the program is running will not change
Some values in the program execution is fixed, and should not be changed.
python this argument is not constant, but programmers convention with all uppercase words as constants. So variables and constants are the same, but the best Do not attempt to change the constants.
Small integer pool
In order to optimize the speed of Python, using a small integer object pooling, avoiding the frequent application is an integer and destruction of memory space. Python definition of small integers is [-5, 256] These objects are integer-established in advance and will not be garbage collected. In a Python program, no matter in which position LEGB integer in, repeat all the variables defined in the same object integer between -5 to 256, the values of these variables are used.
Garbage collection
Reference count the number of times the associated variable value variable name
Clear labeling for solving the problem of circular references when the application is run out of available space will stop the entire program labeled Clear
Generational recovery in order to avoid repeated scans the reference count, then the case of multiple variable experienced scans have not been recovered, the scanning frequency will be reduced.