How to check if some item properties already exist in list before appending

Question

I have a class, and in a list I hold some instances of the class. Before appending a new instance I want to check if x, y are the same with some other item. If x,y exist already in another instance, I want to make another random pair. When I find a pair that is unique I will append the new instance to the list.

What is the most efficient way to check this by using only a list, and checking inside the for loop??

class Vehicle :
    def __init__(self, CoordX, CoordY, Z) :
        self.X=CoordX
        self.Y=CoordY
        self.Z=Z
VehicleList=[]
for i in range (1,15+1):
        obj_x = randint(1,30)
        obj_y = randint (1,20)
        obj_z=randint(1,100)
        If..#Check if [x,y] of item exists in list and Generate new random
        else:
        NewVehicle=Vehicle(obj_x,obj_y,obj_z)

        VehicleList.append(NewVehicle)

score 3 · Accepted Answer · answered Feb 18 '19 at 18:08

Add an __eq__ method for your class Vehicle

class Vehicle:
    def __init__(self, CoordX, CoordY, Z) :
        self.X = CoordX
        self.Y = CoordY
        self.Z = Z

    def __eq__(self, other):
        return self.X == other.X and self.Y == other.Y and self.Z == other.Z

Then check

if NewVehicle not in VehicleList:
    VehicleList.append(NewVehicle)

Related : Elegant ways to support equivalence ("equality") in Python classes

score 1 · Answer 2 · answered Feb 18 '19 at 17:58

You can do it for example like this:

from random import randint

class Vehicle:
    def __init__(self, CoordX, CoordY, Z) :
        self.X = CoordX
        self.Y = CoordY
        self.Z = Z

VehicleList=[]
for i in range (1, 15 + 1):
    obj_x = randint(1, 30)
    obj_y = randint(1, 20)
    obj_z = randint(1, 100)
    while any(v.X == obj_x and v.Y == obj_y and v.Z == obj_z for v in VehicleList):
        obj_x = randint(1, 30)
        obj_y = randint(1, 20)
        obj_z = randint(1, 100)
    NewVehicle = Vehicle(obj_x, obj_y, obj_z)
    VehicleList.append(NewVehicle)

Alain T. · Answer 3 · 2019-02-18T18:25:08.503

0

You could use the next() function ...

if next( (True for obj in VehiculeList if obj.x == obj_x and obj.y == obj_y), False):
    ... the list already contains x,y ...

edited Feb 18 '19 at 18:25

answered Feb 18 '19 at 18:19

Alain T.

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How to check if some item properties already exist in list before appending

3 Answers3