Class Lane

A lane consists of a number of positions that can either contain a vehicle or be empty (i.e. None).

Vehicles move into one end (the largest index) and out of the other end (index 0).

Simplifications of reality: A lane consists of a number of discrete positions and all vehicles take up equal space.

What happens to the lane as time increases?

Observe that a vehicle is moved no more than one position per time step!

Simplification of reality: A vehicle either stands still or moves one place per time step.

What happens at the ends of Lane?

The Lane class does not know what is in front or behind. It is thus "someone else" who makes sure that vehicles enter or leave the lane.

Lane must provide a method to take out the vehicle on the first position and then return the vehicle that was previously there:

There must also be a method that puts a vehicle to the last place:

If you put a vehicle to the last place and it is not free, you will lose what was on that place:

It must also be possible to investigate whether the last place is vacant or not.

The class must include the following methods:

• A constructor __init__(length) that takes the length, i.e. the number of vehicles that can be on the lane. At the beginning there are no vehicles on the lane.
• A method get_first() that returns the vehicle at the first position without deleting it. If the first place is empty, None is returned.
• A method remove_first() that returns and deletes the vehicle in the first place. If the place is empty, None is returned. The method makes no other changes to the Lane object.
• A method step() that moves all vehicles except the first one on the file (index 0) one position forward. A vehicle may only be moved if the next position is vacant. The move should take place from left to right, ie. the vehicle on index 1 is moved first, then vehicle on index 2 is moved, and so on.
• A method is_last_free() that returns True if the last place is free, otherwise False.
• A method enter(v) that places vehicle v at the end of the lane.
• A method number_in_lane() that returns the number of vehicles on the lane.
• The method __str__() that returns an appropriate string representation of the object. See below!

In the main program, the Lane objects must be handled with these methods and thus be independent of the internal representation, i.e. you're not allowed to access or modify the lane's attribute from outside the object, use the methods instead!

Below you can find code with print outs that demonstrate the different methods:

Kod

Utskrift

def demo_lane(): """Demonstration of the class Lane""" a_lane = Lane(10) print(a_lane) v = Vehicle('N', 34) a_lane.enter(v) print(a_lane) a_lane.step() print(a_lane) for i in range(20): if i % 2 == 0: u = Vehicle('S', i) a_lane.enter(u) a_lane.step() print(a_lane) if i % 3 == 0: print(' out: ', a_lane.remove_first()) print('Number in lane:', a_lane.number_in_lane())

[..........] [.........N] [........N.] [.......NS.] out: None [......NS..] [.....NS.S.] [....NS.S..] out: None [...NS.S.S.] [..NS.S.S..] [.NS.S.S.S.] out: None [NS.S.S.S..] [NSS.S.S.S.] [NSSS.S.S..] out: Vehicle(N, 34) [SSS.S.S.S.] [SSSS.S.S..] [SSSSS.S.S.] out: Vehicle(S, 0) [SSSS.S.S..] [SSSSS.S.S.] [SSSSSS.S..] out: Vehicle(S, 2) [SSSSS.S.S.] [SSSSSS.S..] [SSSSSSS.S.] out: Vehicle(S, 4) [SSSSSS.S..] Number in lane: 7

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