python中的类继承

你好，我的练习题是

在自己的文件中创建一个测量类，该文件扩展了测量类。以下是构造函数的标题： 定义初始化（自我，数据库） YPSurvey构造函数将调用Survey类构造函数来创建连接。YPSurvey类将从数据库的连接对象创建自己的私有游标

这就是我的调查课的样子

    """
File survey.py
Accesses the demographics data in a sqlite3 survey database
"""

import sqlite3


class Survey:
    """Represents survey information contained in a Demographic table"""

def __init__(self, database):
    """Constructor creates a Survey object and connects to a
    Survey database using the input database parameter. 
    A cursor is also initialized to execute queries and hold the data.
    Initializes a List for use in retrieving demographic information."""
    self.__databaseName = database
    self.__conn = sqlite3.connect(database)
    self.__cur = self.__conn.cursor()
    self.__demographicList = list()

def __str__(self):
    """Returns the database name"""
    return print("Connected to "+str(self.__databaseName))

def getConn(self):
    """Returns the database connection for use by child class objects"""
    return self.__conn       

def clearDemographicList(self):
    """Clears the demographicList for reuse"""
    self.__demographicList.clear()

def getNumberOfPersonIDs(self):
    """Returns the total number of people who took the survey"""
    self.__cur.execute('Select count(PersonID) from Demographics')
    for row in self.__cur:
        total = row
    return total

def getNumberByDemographic(self, userDemographic):
    """Returns a copy of the demographicList, filled with the number of
    people in a particular demographic.
    Example: if userDemographic = "Gender", demographicList will contain
    a list of tuples with the number of females and males who took the survey"""
    self.clearDemographicList()
    self.__cur.execute("Select "+userDemographic+", count(?) from Demographics group by "
                       +userDemographic,(userDemographic,) )
    for row in self.__cur:
        self.__demographicList.append(row)
    return self.__demographicList

import sqlite3
class YPSurvey_Final:

def __init__(self, database):
    self.__databaseName = database
    self.__conn = sqlite3.connect(database)
    self.__cur = self.__conn.cursor()
    self.__phobiaList = list()
    self.__demographicList = list()
    self.__phobia_nameList = list()


def getNumberOfEachPhobia(self):
    """Returns the total number of people who took the survey"""
    self.__cur.execute("SELECT Phobia, COUNT(*) FROM Phobias GROUP BY Phobia ORDER BY Phobia DESC")
    for row in self.__cur:
        self.__phobiaList.append(row)
    return self.__phobiaList
def phobias(self):
    print('I counted this many phobias: {}'.format(len(self.__phobiaList)))
    for phobia in self.__phobiaList:
        print('Phobia and # of people: {}'.format(phobia))

def phobias_names(self):
    print('There is this many:{}'.format(len(self.__phobia_nameList)))
    for phobias_n in self.__phobia_nameList:
        print ("test",phobias_n)
def clearDemographicList(self):
    """Clears the demographicList for reuse"""
    self.__demographicList.clear()              
def getNumberByDemographic(self, userDemographic, phobia_name):
    self.clearDemographicList()
    self.__cur.execute("SELECT "+userDemographic+", phobia, 1.0 * COUNT(*) / (SELECT COUNT(*) FROM Phobias) AS percentage FROM Demographics,Phobias WHERE Phobia = ? GROUP BY "+userDemographic+"",(phobia_name,))
    for row in self.__cur:
        self.__demographicList.append(row)
    return self.__demographicList

def demographics(self):
    for demographic in self.__demographicList:
        print(demographic)
def phobia_names(self):
    for phobia_name in self.__phobia_nameList:
        print(phobia_name)

这是我的课看起来像

    """
File survey.py
Accesses the demographics data in a sqlite3 survey database
"""

import sqlite3


class Survey:
    """Represents survey information contained in a Demographic table"""

def __init__(self, database):
    """Constructor creates a Survey object and connects to a
    Survey database using the input database parameter. 
    A cursor is also initialized to execute queries and hold the data.
    Initializes a List for use in retrieving demographic information."""
    self.__databaseName = database
    self.__conn = sqlite3.connect(database)
    self.__cur = self.__conn.cursor()
    self.__demographicList = list()

def __str__(self):
    """Returns the database name"""
    return print("Connected to "+str(self.__databaseName))

def getConn(self):
    """Returns the database connection for use by child class objects"""
    return self.__conn       

def clearDemographicList(self):
    """Clears the demographicList for reuse"""
    self.__demographicList.clear()

def getNumberOfPersonIDs(self):
    """Returns the total number of people who took the survey"""
    self.__cur.execute('Select count(PersonID) from Demographics')
    for row in self.__cur:
        total = row
    return total

def getNumberByDemographic(self, userDemographic):
    """Returns a copy of the demographicList, filled with the number of
    people in a particular demographic.
    Example: if userDemographic = "Gender", demographicList will contain
    a list of tuples with the number of females and males who took the survey"""
    self.clearDemographicList()
    self.__cur.execute("Select "+userDemographic+", count(?) from Demographics group by "
                       +userDemographic,(userDemographic,) )
    for row in self.__cur:
        self.__demographicList.append(row)
    return self.__demographicList

import sqlite3
class YPSurvey_Final:

def __init__(self, database):
    self.__databaseName = database
    self.__conn = sqlite3.connect(database)
    self.__cur = self.__conn.cursor()
    self.__phobiaList = list()
    self.__demographicList = list()
    self.__phobia_nameList = list()


def getNumberOfEachPhobia(self):
    """Returns the total number of people who took the survey"""
    self.__cur.execute("SELECT Phobia, COUNT(*) FROM Phobias GROUP BY Phobia ORDER BY Phobia DESC")
    for row in self.__cur:
        self.__phobiaList.append(row)
    return self.__phobiaList
def phobias(self):
    print('I counted this many phobias: {}'.format(len(self.__phobiaList)))
    for phobia in self.__phobiaList:
        print('Phobia and # of people: {}'.format(phobia))

def phobias_names(self):
    print('There is this many:{}'.format(len(self.__phobia_nameList)))
    for phobias_n in self.__phobia_nameList:
        print ("test",phobias_n)
def clearDemographicList(self):
    """Clears the demographicList for reuse"""
    self.__demographicList.clear()              
def getNumberByDemographic(self, userDemographic, phobia_name):
    self.clearDemographicList()
    self.__cur.execute("SELECT "+userDemographic+", phobia, 1.0 * COUNT(*) / (SELECT COUNT(*) FROM Phobias) AS percentage FROM Demographics,Phobias WHERE Phobia = ? GROUP BY "+userDemographic+"",(phobia_name,))
    for row in self.__cur:
        self.__demographicList.append(row)
    return self.__demographicList

def demographics(self):
    for demographic in self.__demographicList:
        print(demographic)
def phobia_names(self):
    for phobia_name in self.__phobia_nameList:
        print(phobia_name)

---

因此，我不明白“扩展调查类”是什么意思，以及如何将我的YP调查类更改为与调查类一起使用？

如果您希望从调查类扩展YP调查最终版，则需要替换YP调查最终版的类定义，如下所示：

class YPSurvey_Final(Survey):
    ....

“extends”通常在OOP中用来表示继承。您可以使您的类从另一个类继承，如下所示：

class MyClass(BaseClass):

def __init__(self):
    super().__init__()

您可以使用

super

方法将调用委托给super-/baseclass构造函数，如下所示：

class MyClass(BaseClass):

def __init__(self):
    super().__init__()