Basic knowledge of Python explained

16th Section MySQLdb

• Win64 bit installation python-mysqldb1.2.5

• Install MySQLdb under Ubuntu

  sudo apt-get install Python-mysqldb

• Import MYSQLDB Library

  Import MySQLdb

• Create a database connection

  conn = MySQLdb.connect (host= "localhost", user= "root", passwd= "123456", db= "test", charset= "UTF8")

• Connect Object Properties

• commit(): If the database table has been modified, commit to save the current data. Of course, if this user does not have permission to do it, nothing will happen.

• rollback(): If you have permission, cancel the current operation, or an error.

• cursor([cursorclass]): Cursor pointer.

• Creating cursors (Pointers) cursor

  cur = conn.cursor ()

• Cursor how to execute the command:

• execute(query, args): Executes a single SQL statement. Query is the SQL statement itself, and args is the list of parameter values. The return value after execution is the number of rows affected.

• executemany(query, args): Executes a single SQL statement, but repeats the parameters in the list of parameters and returns the number of rows affected

• Insert a record in a data table

  Cur.execute ("INSERT into users (Username,password,email) VALUES (%s,%s,%s)", ("Python", "123456", "python@gmail.com")

• Inserting multiple records in a data table

  Cur.executemany ("INSERT INTO Users" (Username,password,email) VALUES (%s,%s,%s), (("Google", "111222", "g@gmail.com"), ("Facebook", "222333", "F@face.book"), ("GitHub", "333444", "git@hub.com"), ("Docker", "444555", "doc@ker.com"))

• Commit Database Operations

  Conn.commit ()

• Querying data

  Cur.execute ("SELECT * from users")

• fetchall(self): Receives all the returned result rows.

• fetchmany(size=None): Receives a size bar to return the result row. If the value of size is greater than the number of result rows returned, the cursor.arraysize data is returned.

• fetchone(): Returns a result row.

• scroll(value, mode='relative'): Moves the pointer to a row. If mode= ' relative ', the value bar is moved from the current row, and if mode= ' absolute ', the value bar is moved from the first row of the result set.

  Cur.execute ("SELECT * from users") lines = Cur.fetchall () for line in lines:    print Linecur.execute ("SELECT * from Users where id=1 ") Line_first = Cur.fetchone ()     #只返回一条print line_firstcur.execute (" SELECT * from users ") print Cur.fetchall ()

• Cursor object methods to get data

• Cursors cursor Operations

• cur.scroll(n)Or cur.scroll(n,"relative") : means move up or down relative to the current position, n is positive, indicates down (forward), n is negative, indicates up (backward)

• There is also a way to achieve "absolute" movement, not "relative" movement: Add a parameter "absolute"

  Cur.scroll (1) cur.scroll ( -2) Cur.scroll (2, "absolute")    #回到序号是2, but pointing to the third article

• Update data

  Cur.execute ("Update users set username=%s where id=2", ("Mypython")) Conn.commit ()

• Specify the database

  conn = MySQLdb.connect ("localhost", "root", "123456", port=3306,charset= "UTF8")    #创建数据库时不指定那个数据库conn. select_db (" Test ")      #连接创建后再指定

• Close the database

  Cur.close ()     #先关闭游标conn. Close ()    #再关闭数据库

Section 17th Object Oriented

Classes and objects

• Process-oriented and object-oriented programming

• Process-oriented programming: Functional programming, C-programs, etc.

• Object-Oriented Programming: C++,java,python, etc.

• Classes and objects: Two important concepts in object-oriented

• Class: Is the abstraction of things, such as: Car models

• Object: Is an instance of a class, for example: QQ sedan, bus

• Example description

• Car models can abstract the characteristics and behavior of a car, and then instantiate a real car entity to come out

Python class definition

• Definition of Python class

• Define a class using the class keyword, and capitalize the first letter of the class name

• When a programmer needs to create a type that cannot be represented by a simple type, you need to create a class

• Classes combine the required variables and functions, which are also known as "encapsulation"

• Structure of the Python class

  Class Name:    member Variable    member function Class MyClass (): First    = 123    def fun (self):        print "I am function"

• Creation of objects

• Handles are used to distinguish between different objects

• The properties and methods of an object correspond to member variables and member functions in a class

  if __name__ = = "__main__":    MyClass = MyClass ()     #创建类的一个实例

• The process of creating an object is called instantiation; When an object is created, it contains three aspects of the attribute: the handle, property, and method of the object.

• Constructor __init__

  Class Person:    def __init__ (self, name, Lang, website):        self.name = name        Self.lang = lang        self.website = website

• Self is a very magical parameter.

• Self points to an instance of the class, and when the instance calls the method, self points to the instance of the method that is called

• Subclass, parent class, and inheritance

  # abstract Shape Classes Class shape: # class Properties Edge = 0 # constructor def __init_ _ (Self, edge): Self.edge = method of the Edge # class Def Getedge (self): return Self.edge # abstract method def getarea ( Self): pass# Triangle class, inheriting abstract shape class Triangle (shape): width = 0 height = 0 # constructor def __init__ (self, width, he ight): #调用父类构造函数 shape.__init__ (self, 3) Self.width = width Self.height = height #重写方法 D EF Getarea (self): return Self.width * self.height/2# Quad class, inheriting abstract shape classes class Rectangle (shape): width = 0 He  ight = 0 # constructor def __init__ (self, width, height): #调用父类构造函数 shape.__init__ (Self, 4) self.width = width Self.height = height #重写方法 def getarea (self): return self.width * self.heighttriangle = Trian GLE (4,5);p rint Triangle.getedge () print triangle.getarea () rectangle = Rectangle (4,5);p rint Rectangle.getedge () print Rectangle.getarea () 

• Python supports multiple inheritance, but it is not recommended to use