Python_ Fundamentals of computer

One .python 2 .X  VS  3.X

    1. 2.x = Default encoding =ASSIC = I won't support it ,3.x = Default encoding =UNICODE = Chinese is supported by default

     2. 3.x Are not compatible 2.x      3.3.x Core grammar adjustments , Easier to learn      4. The new feature defaults to 3.x There are

Two . Variable

In order to store some intermediate points in the operation of the program result , In order to facilitate future calls ,python The variable name is represented in lowercase , Upper case means constant name

# Variable in lowercase
age = 27
# Constant in uppercase
NAME = xiaoming

Naming rules for variables

    1. Be descriptive （ for example ：myage）     2. Variable names can only be , Numbers , Alphabetic composition , It can't be spaces or special characters (#?<.,￥$*!~)     3. Cannot use Chinese as variable name     4. Cannot start with a number     5. Reserved characters cannot be used

3、 ... and . code

The first table that supports Chinese is called GB2312

    1980 The year was born gb2312 6700+

    1995 The year was born gbk1.0 20000

    2000 The year was born gb18030 27000

    unicode unicode   Support coding for all countries and regions

    UTF-8 = unicode The extended set of , Variable length character coding set

Code evolution process

Assic -->Gb2312 ->gbk1.0-->gb18030

Assic -->unicode -->utf-8   /utf-16

Python2.x == Assic Default encoding , You need to start writing code , Define the encoding type #!-- coding:utf-8 -- perhaps #coding:utf-8

#!-*- coding:utf-8 -*- 

python3.x == unicode Default encoding

unicode It's downward compatible gb2312 , gbk

Four . notes

Single-line comments use #

#str string = character string To convert data into a string, use str( Transferred data )
print("You can still live for " + str(death_age - int(age)) +" years ....")

Multiline comments use three single quotes or three double quotes ''' Annotated content '''

'''
if guess_age == age_of_princal then
print("yes")
else
print("no ")
'''