Explanation of python basic knowledge points

Section 16 MySQLdb

• ##win64-bit installation python-mysqldb1.2.5

• Installing MySQLdb under ubuntu

  sudo apt-get install python-MySQLdb

• Import MySQLdb library

  import MySQLdb

• Create database connection

  conn = MySQLdb.connect(host="localhost",user="root",passwd="123456",db="test",charset="utf8")

• connect object properties

• commit(): If the database table is modified, submit to save the current data. Of course, if this user doesn't have permission and just does it, nothing will happen.

• rollback(): If you have permission, cancel the current operation, otherwise an error will be reported.

• cursor([cursorclass]): Cursor pointer.

• Create a cursor (pointer) cursor

  cur = conn.cursor()

• cursor method of executing commands:

• execute(query, args): Execute 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 affected rows.

• executemany(query, args): Execute a single sql statement, but repeatedly execute the parameters in the parameter list, and the return value is the number of affected rows

• Insert a record into the data table

  cur.execute("insert into users (username,password,email) values (%s,%s,%s)",("python","123456","python@gmail.com"))

• Insert multiple records into the 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")))

• Submit database operation

  conn.commit()

• Query data

  cur.execute("select * from users")

• ##fetchall(self)

  :Receive all Return result rows.

• fetchmany(size=None)

  : Receive size return result rows. If the value of size is greater than the number of returned result rows, then Will return cursor.arraysize pieces of data.

• fetchone()

  : Returns one result row.

• scroll(value, mode='relative')

  : Move the pointer to a certain row. If mode='relative', it means moving the value bar from the current row. If mode='absolute', it means moving the value bar from the result set. The first line moves the value bar.<pre class="brush:php;toolbar:false">cur.execute(&quot;select * from users&quot;) lines = cur.fetchall() for line in lines:     print line cur.execute("select * from users where id=1") line_first = cur.fetchone()     #只返回一条 print line_first cur.execute(&quot;select * from users&quot;) print cur.fetchall()</pre>

The method of cursor object to obtain data

The operation of cursor
• cur.scroll(n)

  or cur.scroll(n,"relative"): means to move up or down relative to the current position , n is a positive number, which means downward (forward), n is a negative number, which means upward (backward)

There is another way to achieve "absolute" movement, not " Relative" move: Add a parameter "absolute"

• cur.scroll(1)
  cur.scroll(-2)
  cur.scroll(2,"absolute")    #回到序号是2,但指向第三条

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 17 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: are two important concepts in object-oriented
Class: is an abstraction of things, such as: car model
Object: is an instance of a class, such as: QQ car, bus

Example description
The car model can abstract the characteristics and behavior of the car, and then instantiate a real car entity Come out

Python class definition

Python class definition
Use the class keyword to define a class, and the first letter of the class name should be capitalized
When programmers need to create a type that cannot be represented by a simple type, they need to create a class
A class combines the required variables and functions. This inclusion is also called "encapsulation"

The structure of the Python class

• class 类名：
      成员变量
      成员函数
  
  class MyClass():
      first = 123
      def fun(self):
          print "I am function"

Creation of objects
Handles are used to distinguish different objects
Properties of objects And methods correspond to member variables and member functions in the 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 characteristics: Object handles, properties and methods.

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. When the instance calls a method, self points to the instance of the called method

Subclass, parent class and inheritance

• # 抽象形状类
  class Shape:
      # 类的属性
      edge = 0
      # 构造函数
      def __init__(self, edge):
          self.edge = edge
      # 类的方法
      def getEdge(self):
          return self.edge
      # 抽象方法  
      def getArea(self):
          pass
  
  #三角形类，继承抽象形状类
  class Triangle(Shape):
      width = 0
      height = 0
      # 构造函数
      def __init__(self, width, height):
          #调用父类构造函数
          Shape.__init__(self, 3)
          self.width = width
          self.height = height
      #重写方法
      def getArea(self):
          return self.width * self.height / 2
  
  #四边形类，继承抽象形状类       
  class Rectangle(Shape):
      width = 0
      height = 0
      # 构造函数
      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.height
  
  triangle = Triangle(4,5);
  print triangle.getEdge()
  print triangle.getArea()
  
  rectangle = Rectangle(4,5);
  print rectangle.getEdge()
  print rectangle.getArea()

Python supports multiple inheritance, but it is not recommended

The above is the detailed content of Explanation of python basic knowledge points. For more information, please follow other related articles on the PHP Chinese website!