The difference between Python's base 2 and 3, and the For and while loops

1, the difference of Python2\python3: Python2\python3 difference:
One, code duplication, Python2 code repetition function reuse, inclusion of other language parts, not standardized
Python3 to be integrated, simple and beautiful
Compile: Compile all the code into binary once and then run it again.
Cons: Low development efficiency, no cross-platform

Interpreted: When the program starts executing, the code is interpreted as a line of binary, executed.
Cons: Low development efficiency

Python is a bit:
1, the development of high efficiency, by the third-party library directly call, such as PHP can not connect
2. Portability
3, expandable, embeddable High: Join the C language speed to execute fast

Types of Python:
CPython: The most widely used, first converted into C bytecode, to the system
Jpython: Byte code converted to Java, to system
Other languages Python: all the same, convert to the corresponding byte code
PyPy: The code is converted to bytecode all at once and then to the system

Second, the Python2 uses the ASCII, does not recognize the Chinese: Python3 uses the utf-8 character
Three, Python2 has a long int i 3 no
Four, python2 in print can not add () but 3 to add ()
Five, 2 is raw_input equals 3 of input

2. Variables: Variables:
The results of the operation in the program are charged to the memory for easy follow-up transfer:
Cannot start with a number, cannot be a python keyword, and a digital letter underline is arbitrary
Variables to have a gram of descriptive
Variable do not use Chinese
Variable cannot be too long
A = 1
b = 2 .....
All can
3, constant: constant:
Constant amount: π, xxx number
All uppercase variables are constants and placed at the top of the file
Opent_work = 323423, this is the constant
4. Note: note:
Single Use #
Multiple lines "" "" "" "or" "

5. Basic Data type:
int numeric type calculation. Algorithms such as subtraction

STR: string is quoted in quotation marks.
What data type is a type (object)
Useful: Store simple small amounts of data
Large range with double quotes, small range with single quotes
Multiple lines can use three quotes, such as product list, multi-line
can add + string concatenation, and multiply str string numeric type

Boolean value,
True and Flase
0 for Flase The others are true
6, Input:
Interacting with the user, input comes out of a string
Input ("description information")

7. Formatted output:
% placeholder%s string%d number
If you use%, you must escape the percent in addition
If you want to convert a string to a number, you can wrap it with an int (variable), and the string must be all numbers.

Name = input ("name")
Age = Input ("Age")
Job = input ("job")
Hobby = input ("hobby")

Meg= "" "------------info of%s-----------
Name:%s
Age:%d
Job:%s
Hobbie:%s
-------------End-----------------
"" "% (name,name,int (age), Job,hobby)
Print (MEG)

8. If statement:

If condition:
Results
Here is an example of a TAB key or four spaces in the result here
Two Equals is the comparison = =, one = is the assignment

If condition:
Meet conditional execution Code
Elif Conditions:
The above conditions are not satisfied.
Elif Conditions:
The above conditions are not satisfied.
Elif Conditions:
The above conditions are not satisfied.
Else
All the above conditions are not satisfied, go this part.

9. While
A = 1
Flag = True
While flag:
Print (a)
A = A+1
If a ==5050:
Flag = False

Note: The flag here is used for two loops to jump out of a stop
Break: Jump out of the loop with his column
Continue: Ends this loop, but also executes

10. Logical operators:
And Or not

() "Not" and "or
Priority level
1 > 2 and 3 < 4 or 4 > 5 and 2 > 1 or 9 < 8
1 > 1 and 3 < 4 or 4 > 5 and 2 > 1 and 9 > 8 or 7 < 6

11. Code:
Electrical signal 01010101010101010
Computer:
A ' SIIC code 128
7-bit identification of one byte
Upgrade to 8 bits a byte 256 2 of the 8-time Square
00000001 = = = one character
Universal code AH: Unicode includes all countries
16 bytes Represents a character
00000001 00000001 = = 2 of a character 16 Times Square

Change: 4 byte table one character is 32 times
11111111 11111111 11111111 11111111 represents a byte 2 of the 32-time Square
Waste of resources:

Upgrade Utf-8: Minimum 8-bit:
English 8 bit one byte, 00000001
Europe 16 bits Two bytes, 00000001 00000001
Asia 24 bits Three bytes, 00000001 00000001 00000001

Conversion of units:
8bit ==1bytes
1024bytes ==1kb
1024KB ==1MB
1024MB = = 1G

Utf-16 a minimum of 16 characters

Underlying data type:
Dict Dictionary
dict:{' name ': ' xxx ', ' Age ': 13}
Print (dict[' name '])
can print out xxx
Key values can be numbers and strings, lists, etc.

The difference between Python's base 2 and 3, and the For and while loops