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Python: A class attribute is being copied to all my instances of that class in a for-loop

I have a class called Station...

Station

class Station():
def __init__(self):
self.connecting_stations =


...a list with 3 Station instances...

Station

stations = [Station() for n in range(3)]


...and a for-loop that appends the string "New Hampshire" to the connecting_stations attribute of my three Station instances.

"New Hampshire"

connecting_stations

Station

for station in stations:
station.connecting_stations.append("New Hampshire")


When I print([station.connecting_stations for station in stations]) it prints:

print([station.connecting_stations for station in stations])

[
["New Hampshire", "New Hampshire", "New Hampshire"],
["New Hampshire", "New Hampshire", "New Hampshire"],
["New Hampshire", "New Hampshire", "New Hampshire"]
]


...i.e. the connecting_stations attribute of all of my Station instances have the same "New Hampshire" repeated 3 times.

connecting_stations

Station

"New Hampshire"

But what I really wanted to do is:

>>> print(stations[0].connecting_stations)
["New Hampshire"]
>>> print(stations[1].connecting_stations)
["New Hampshire"]
>>> print(stations[2].connecting_stations)
["New Hampshire"]


...i.e. I want each one of my Station instances to have one -- only one -- connecting station, which is called "New Hampshire", but actually they're getting 3 "New Hampshire" strings each.

Station

"New Hampshire"

"New Hampshire"

How is that even possible? What is happening and how can I solve my problem?

Note: Sorry for the bad title. Did not find better and shorter words to describe my problem.

[Station()] * 3

Station

1 Answer
1

Seems like you're not adding 3 different instances of your class to the list, but the same instance, and then when you modify it 3 times, you get "New Hapmshire" added to this same instance 3 times.

Try to replace:

for station in stations:
station.connecting_stations.append("New Hampshire")


with

stations[0].connecting_stations.append("New Hampshire")


and print your list again to see =)

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