Python's basic syntax, covering data types, looping judgments, lists, maps, set, and more

#the statement at the beginning is a comment

When the statement ends with a colon ":", the indented statement is treated as a block of code. Generally indent 4 spaces

The Python program is case-sensitive, and if the case is written incorrectly, the program will error.

Data types for Python

• Integral type
• Floating point Type
• String
• Boolean value
• Null value

Variable

This block of variables needs to be well explained. Python is a dynamic language, its variables do not require a specified type, and Java is a static language, and to use a variable, you must specify the type for the variable.

In this case, the Python variable is simple, like this:

A = 3

x = "Hello"

And so on are variables.

A Python string

Because Python was born earlier than the Unicode standard, the earliest Python only supported ASCII encoding, and ordinary strings were ‘ABC‘ ASCII-encoded inside python. Python provides the Ord () and Chr () functions to convert letters and corresponding numbers to each other:

>>> ord(‘A‘)65>>> chr(65)‘A‘

Python later added support for Unicode, expressed in Unicode as a string u‘...‘ , for example:

>>> print u‘中文‘中文>>> u‘中‘u‘\u4e2d‘

Because the Python source code is also a text file, so when your source code contains Chinese, it is important to specify that you save it as UTF-8 encoding when you save it. When the Python interpreter reads the source code, in order for it to be read by UTF-8 encoding, we usually write these two lines at the beginning of the file:

#!/usr/bin/env python# -*- coding: utf-8 -*-

The first line of comments is to tell the Linux/os x system that this is a python executable and the Windows system ignores this comment;

The second line of comments is to tell the Python interpreter to read the source code according to the UTF-8 encoding, otherwise the Chinese output you write in the source code may be garbled.

Formatting of strings

In Python, the format used is consistent with the C language, and is implemented as an % example:

>>> ‘Hello, %s‘ % ‘world‘‘Hello, world‘>>> ‘Hi, %s, you have $%d.‘ % (‘Michael‘, 1000000)‘Hi, Michael, you have $1000000.‘

As you may have guessed, the % operator is used to format the string. Inside the string, the representation is replaced by a string, which %s %d is replaced with an integer, there are several %? placeholders, followed by a number of variables or values, the order to correspond well. If there is only one %? , the parentheses can be omitted.

Common placeholders are:

%d	Integer
%f	Floating point number
%s	String
%x	hexadecimal integer

Another way to output string concatenation is to use the Format method.

Name = "Kobayashi"

Age = 25

Sex = "male"

Print (' My name is {0}, is a {1} born, this year {2} years old '. Format (name,sex,age))

Python input and output

Output:

Print ()

Input:

Name = Raw_input ()

List types for Python

1 #Encoding:utf-82 3 #There are two kinds of data collection types built into the Pythton, one is list, and the other is a tuple4 5 #List is an ordered set, you can query, add, delete, modify the list6 7 #A tuple is a tuple that has a sequence table. Unlike list, the contents of a tuple cannot be modified, so it has no method to add, modify, or delete. 9  Ten  One #1. List A  -MyList = ['a','b', 123,'ABC'] -  the Print(myList)  -  + #query operation for 1.1 list -  + Print(Mylist[0])#Get the element of list by index, get the first element A  at Print(Mylist[-1])#get the last element in a list -  - Print(Len (myList))#get the length of a list -  -   -  in #1.2 The Add operation of the list -  toMylist.append ('D')#append an element at the end of the list +  -Mylist.insert (2,'Insert Element')#add an element at the specified position in the list the  *   $ Panax Notoginseng #1.3 The delete operation of the list -  theMylist.pop ()#Delete the element at the end of the list +  AMylist.pop (2)#deletes the element at the specified position in the list the  +   -  $ #1.4 List's modification operation $  -Mylist[0] ="AAA" #modifies the value of a specified position in a list -  the   - Wuyi #1.5 multi-dimensional arrays the  -List_tmp = ['1','2'] Wu  -Mylist.append (LIST_TMP)#You can insert another list in a list About  $ Print(Mylist[4][1])#you can get the elements of the inner class table by specifying the following table -  -   -  A #2. Tuple +  the #What is the meaning of immutable tuple? Because the tuple is immutable, the code is more secure. If possible, you can use a tuple instead of a list as much as possible.  -  $Mytuple = ('a','b', 123,'ABC') the  the   the  the #Query operations for 2.1 tuple -  in Print(mytuple[0]) the  the Print(Mytuple[-1])#a tuple gets an element that operates like a list About  the   the  the #2.2 A tuple's trap +  - #When you define a tuple, the elements of the tuple must be determined at the time of definition. the Bayit = ()#to define an empty tuple the  thet = (1)#to define a tuple with only 1 elements, if you define it this way: the result is 1. -  - #The definition is not a tuple, is 1 this number! This is because parentheses () can represent both tuples and parentheses in mathematical formulas, which creates ambiguity. the  the ## As a result , Python specifies that, in this case, the parentheses are calculated and the result is naturally 1.  the  the #therefore, only 1 elements of a tuple definition must be added with a comma, to eliminate ambiguity: -  thet = (1,)#this defines the result as (1,) the  the #Python will also add a comma when displaying a tuple of only 1 elements, lest you misunderstand the parentheses in the mathematical sense. 

Python's judgment loop

#the Python loop. One is a for loop, one is a while loop#For Loop, read out the list elementnames= ["AA","BB","cc","DD"] forNameinchnames:Print(name)#while loop, calculates the sum of the elements in the listarr= Range (101) n=0sum=0 whileN <Len (arr): Sum+=Arr[n] n+=1Print(sum)#Python's judgment. To achieve a good judgment of the differencescore= Int (raw_input ())#coercion of type conversions, Raw_input reads always in the form of a stringif(Score >=90 andScore <=100):    Print("Excellent")elif(score>=70 andScore<90):    Print("Good")elif(score>=60 andScore<70):    Print("General")elif(score>=0 andScore <60):    Print("inferior lattice")Else:Print("Please enter the correct score! ")

Python's dict and set

Python built-in dictionary: dict support, Dict full name dictionary, in other languages also known as map, using key-value (Key-value) storage, with a very fast search speed.

It is important to use dict correctly, and the first thing to keep in mind is that the Dict key must be an immutable object .

Dict is unordered, equivalent to the HashMap in Java

1Mydict = {"AA": 92,"BB": 85,"cc": 56,"DD": 64}2 3 #Dict's Search4 5  forKinchmydict:6 7     Print("%s got%d points"%(K,mydict.get (k)))8 9 #Modification of DictTen  Onemydict["AA"] = 100 A  - Print(mydict["AA"]) -  the #additions and deletions of dict -  -mydict["ee"] = 88#additions to Python -  +Mydict.pop ("ee")#Delete -  + Print(Mydict.get ("ee"))#return None

Set is similar to Dict and is a set of keys, but does not store value. Because key cannot be duplicated, there is no duplicate key in set.

Equivalent to HashSet in Java

1 myset = ([1,2,3,4])23for in# traversal 4 5     Print (k) 6 7 # Append 8 9 # removed from

Python's basic syntax, covering data types, looping judgments, lists, maps, set, and more