Summary of basic knowledge of python

First, the advantages and disadvantages of python

　　advantage:

1. Beautiful, clear, simple
2. high level language
3. High development efficiency
4. Portability, Extensibility, Embeddability

　　shortcoming:

1. running slow
2. Code cannot be encrypted
3. Threads cannot take advantage of multiple CPUs

Second, the difference between python2 and python3

　　Code:

1. python2: code confusion, more repetitive code, redundant
2. python3: code advocating beauty, clarity and simplicity

　　print：

1. python2: print is a statement
2. python3: print is a function

　　input：

1. python2: raw_input() receives strings, input() receives numbers
2. python3: input() receives all strings

　　Encoding:

1. python2: The default encoding is ASCII code (if you want to use Chinese: #_*_coding:utf-8_*_)
2. python3: The default encoding is utf-8, which supports Chinese

　　Inequality operator:

1. python2: you can use != or ><
2. python3: only use !=

　　Create an iteration counter:

1. python2：xrange
2. python3：range

　　repr：

1. python2: repr can be a statement
2. python3: only repr() function is allowed

　　document:

1. python2: you can use != or ><
2. python3: only use !=

　　Integer:

1. python2: there is a long type
2. python3: all are int

　　Modify the syntax:

1. python2: dictionary keys, values, items and map, filter, reduce return a list
2. python3: dictionary keys, values, items and map, filter, reduce return an iterable object

　　Added syntax:

1. python2: print and exec statements, no methods like nolocal
2. python3: print and exec are changed to functions, new methods such as nolocal are added

　　inherit:

1. python2: default classic class (required for new-style classes (object))
2. python3: only new-style classes

3. Types of Development

　　compiled

　　Disadvantages: slow troubleshooting, low development efficiency, not portable

　　Advantages: high execution efficiency

　　Typical: C language, go language

　　interpretive

　　Disadvantage: low execution efficiency

　　Advantages: fast troubleshooting, high development efficiency, portability

　　Typical: python, PHP

　　Hybrid

　　Typical: java, C#

4. Types of python

　　Cpython: based on C language development

　　lpython

　　Jpython

　　PyPy: currently the fastest performing

5. Variables and constants

　　Constant: a constant that remains unchanged, commonly known by convention, all capitalized as constants

 

　　Variables: Store the running results of the program in memory for later code calls

　　Require:

1. Must consist of numbers, letters, and underscores
2. cannot start with a number
3. cannot be a keyword
4. Can't be Chinese, can't be too long, must be descriptive
5. The official website recommends underscore old_boy and hump OldBoy

6. Statement

　　if statement

　　　elif branch judgment

　　while statement

　　　flag (flag bit)

　　　break (completely ends the loop)

　　　continue (jump out of this loop)

　　　else (the loop exits execution normally)

　　for statement　

　　　break (completely ends the loop)

　　　continue (jump out of this loop)

　　　else (the loop exits execution normally)

　　in，not in

s = ' old boy alexwusir ' 
print ( ' old boy '  in s)     # True 
print ( ' old boy wusir '  in s)     # False 
print ( ' old boy '  in s)     # True 
print ( ' old boy '  not  in s )     # False

#The result shows that in a string, the defined substring contained in a parent string must be True if it is continuous, False if it is not continuous, in means inclusion, not in means non-inclusion

7. Logical operators

# and or not #The 
first type: before and after are all comparison operations. 
#Priority : () > not > and > or the same priority, calculated from left to right. 
print (1 > 2 and 3 < 4 and 3 > 2 or 2 < 3 ) # True
 print (2 > 1 and 3 < 4 or 4 > 5 and 2 < 1 ) # True
 print (1 > 2 and 3 < 4 or 4 > 5 and 2 > 1 or 9 < 8 ) # False #The
 second type: both front and back are numerical operations. 
'''
x or y if x True,则 return x,否则 return y
'''
print(1 or 3)　　# 1print(2 or 3)　　# 2
print(0 or 3)　　# 3
print(-1 or 3)　　# -1
print(1 and 2)　　# 2
print(0 and 2)　　# 0

#The third type: mix. 
print (1 > 2 or 3 and 4 ) # 4
 print (2 or 2 > 3 and 4 ) # 2
 print (0 or 2 > 3 and 4 ) # False

#Data type conversion: 
'''
int ---> bool non-0 is True, 0 is False
bool---> int  True  1  False 0
print(int(True))
print(int(False))
print(bool(100))
print(bool(0))
'''

Eight, formatted output

# % placeholder s str string d digit number 
# The first type: 
name = input( ' Please enter your name: ' )
age = input( ' Please enter your age: ' )
hobby = input( ' Please enter your hobby: ' )
msg = ' My name is %s, I am %d this year, and my hobby is %s ' % (name,int(age),hobby)
 print (msg)
 #The second 
dic = { ' name ' : ' old boy ' , ' age ' :51, ' hobby ' : ' It doesn't matter ' }
msg = ' My name is %(name)s, this year is %(age)d, and my hobby is %(hobby)s ' % dic
 print (msg)

# Simply displaying % in formatted output is resolved with %%. 
name = input( ' Please enter your name: ' )
age = input( ' Please enter your age: ' )
msg = ' My name is %s, I am %d, and my learning progress is 1%% ' % (name,int(age))
 print (msg)

9. Coding

　　1. Telegram: Didi Didi is actually a high and low level.
　　　Codebook :
　　　today 0000 0001
　　　days 0000 0101
　　　drink 0000 0011
　　　wine 0000 1100
　　　go to 0001 1010
　　　ya 0001 0001

　　　0010010 1000011 1100101 010001

　　2, when the computer stores and transmits, 01010101
　　      initial codebook:
　　　　asiic contains numbers. Eight bits
　　　　01000001 01000010 01000011 ABC
　　　　8 bits = 1 byte represents a character.

　　　　Universal code unicode, the language of all countries is included in this codebook.
　　　　Initial: 16 bits, two bytes, representing one character.
　　　　A: 00010000 00010010
　　　　Medium: 00010010 00010010
　　　　Upgrade: 32 bits, four bytes, representing one character.
　　　　A: 00010000 00010010 00010000 00010010
　　　　Medium: 00010010 00010010 00010010 00010010
　　　　Resource waste.

　　　　Upgrade: utf-8. At least 8 bits (one byte) are used to represent one character.
　　　　English: a :00010000 represents a character with 8 bits.
　　　　Europe: 00010000 00010000 16-bit two bytes represent a character.
　　　　In Asia: 00010000 00010000 00010000 24 bits, three bytes represent one character.

　　　　utf-16

　　　　gbk: GB.
　　　　Contains only: English and Chinese.
　　　　English: a: 00010000 8 bits, one byte represents one character.
　　　　Chinese: Medium: 00010000 00010000 16 bits, two bytes represent one character.
　　　　gb2312.....

　　　　8 bits = 1byte
　　　　1024byte=1kb
　　　　1024kb = 1MB
　　　　1024MB = 1GB
　　　　1024GB = 1TB

　　Python basic mind map link: https://www.processon.com/view/link/5ae71b80e4b019d3a919be99