根据特定属性对类进行排序

Question

我想将类的实例存储到文件中，然后读取数据并根据特定属性以升序显示。

Description of the class: vehicle 
Attributes: vehicle type, fuel type, cost 
Methods: GetVdata(), ShowVdata() 

我一直无法根据成本要求对输出数据进行排序。

​import pickle 

class vehicle: 
    vehicletype = '' 
    fueltype = '' 
    cost = 0 
    def __init__(self, vehicletype = '', fueltype = '', cost = 0): 
     self.vehicletype = '' 
     self.fueltype = '' 
     self.cost = 0 
    def GetVdata(self): 
     self.vehicletype = raw_input("enter the vehicle type: ") 
     self.fueltype = raw_input("enter the fuel type: ") 
     self.cost = input("enter the cost of the vehicle: ") 
    def ShowVdata(self): 
     print "vehicle type : ", self.vehicletype, "\n" , "fuel type: ", self.fueltype , "\n", "cost : ", self.cost 
#v = vehicle() 
#v.GetVdata() 
#v.ShowVdata() 


dat1 = vehicle("4 wheeler", "diesel" , 2000000) 
dat2 = vehicle("2 wheeler", "petrol" , 100000) 
dat1.GetVdata() 
dat2.GetVdata() 


File = open('transport.dat' , 'wb') 
pickle.dump(dat1, File) 
pickle.dump(dat2, File) 
File.close() 

dat1 = vehicle() 
File = open('transport.dat','rb') 
try: 
    while True: 
     print"\n" 
     output = pickle.load(File) 
     output.ShowVdata() 
except EOFError: 
    File.close() 

Answer 1

为了根据其属性的类的对象进行排序，你可以使用operator.attrgetter方法。但是，如果您不想导入任何内容，只需将对象的cost属性放入列表中，然后对该列表进行排序。然后根据那个找到对应的对象dump。这里有一个工作代码：

import pickle 
class vehicle: 
    def __init__(self, vehicletype, fueltype, cost): 
     self.vehicletype = vehicletype 
     self.fueltype = fueltype 
     self.cost = cost 
    def GetVdata(self): 
     self.vehicletype = raw_input("enter the vehicle type: ") 
     self.fueltype = raw_input("enter the fuel type: ") 
     self.cost = input("enter the cost of the vehicle: ") 
    def ShowVdata(self): 
     print "vehicle type : ", self.vehicletype, "\n" , "fuel type: ", self.fueltype , "\n", "cost : ", self.cost 

dat1 = vehicle("4 wheeler", "diesel" , 2000000) 
dat2 = vehicle("2 wheeler", "petrol" , 1000000) 
dat3 = vehicle("2 wheeler", "petrol", 5000000) 
dat4 = vehicle("4 wheeler", "diesel", 3000000) 

data = [dat1, dat2, dat3, dat4] 
costs = [i.cost for i in data] 
costs.sort() 

File = open('transport.dat' , 'wb') 

for value in costs: 
    for i in range(len(data)): 
     if data[i].cost == value: 
      pickle.dump(data[i], File) 
File.close() 

File = open('transport.dat','rb') 
try: 
    while True: 
     print"\n" 
     output = pickle.load(File) 
     output.ShowVdata() 
except EOFError: 
    File.close() 

现在，如果你运行它，你会得到：

vehicle type : 2 wheeler 
fuel type: petrol 
cost : 1000000 


vehicle type : 4 wheeler 
fuel type: diesel 
cost : 2000000 


vehicle type : 4 wheeler 
fuel type: diesel 
cost : 3000000 


vehicle type : 2 wheeler 
fuel type: petrol 
cost : 5000000