Hello all,
NB Noob alert ... !
I am trying to use recursion in a Python class method, but with limited results.
I'm trying to build a car class, with very basic attributes: id, position in a one lane road (represented by an integer), and velocity. One of the functions I have is used to return which car id is in front on this one -- i.e. if we have class:
class Car:
def __init__(self, position, id, velocity):
self.position = position
self.id = id
self.velocity = velocity
Now, I've come up with the following class method (additional details below the code):
def findSuccessorCar(self, cars):
successorCar = ""
smallestGapFound = 20000000
for car in cars:
if car.id == self.id: continue
currentGap = self.calculateGap(car)
if (currentGap > -1) and (currentGap < smallestGapFound):
smallestGapFound = currentGap
successorCar = car
if successorCar == "":
return 1 # calling code checks for 1 as an error code
else:
return successorCar
The plan is to create car objects, then store them in a list. Each time the findSuccessorMethod is called, this global list of cars is passed to it, e.g.
c1 = testCar.Car(4, 5, 1) # position, pos_y, Vel, ID
c2 = testCar.Car(7, 9, 2)
c3 = testCar.Car(9, 1, 2)
cars = [c1, c2, c3]
c1_succ = c1.findSuccessorCar(cars)
This works fine: the find successor car function will say that car c2 is in front of car c1 (position 7 ahead of position 4).
However, I want car c1 to work out what car is in front of its immediate successor -- that is, which car is in front of the car in front, which in this case is car c3. My thinking was that if I did c1_succ.findSuccessorCars(cars) then this should work fine: doing type(c1_succ) shows it is an instance and hasattr shows that it has the anticipated object attributes.
However, when I do try to execute c1_succ.findSuccessorCars(cars), an integer is returned. Hence, I am confused -- why doesn't this work? Why can you not recursively execute a class method in this fashion? Where does this integer come from?
NB Gut feel says that this has something to do with the self declaration, and that I'll need to modify my code so that as well as a global list of cars, there'll need to be a global list of their current positions, or another class method, e.g. findSuccessorsSuccessor (yes, fully aware of crummy naming!). However, I am interested to understand why this recursive approach does not work.
UPDATE
Here is the requested code for calculating a gap between 2 cars -- I appreciate it is very basic, so not too much laughter at the back please.
def calculateGap(self, car):
''' Calculate the gap between two cars
'''
thisCar = self
otherCar = car
gap = otherCar.position_x - thisCar.position_x
return gap