Question

I’m writing my first python program and I’m running into something that seems strange.

My program looks like this:

def main():
  listOfThings = []
  for i in range(0,3):
    newThing = thing()
    newThing.listOfStrings.append('newString')
    listOfThings.append(newThing)

Thing simply looks like this:

class thing:
  listOfStrings = []

I’m expecting listOfThings to be:

listOfThings
 -thing1
  -newString
 -thing2
  -newString
 -thing3
  -newString

But instead i’m getting this:

listOfThings
 -thing1
  -newString
  -newString
  -newString
 -thing2
  -newString
  -newString
  -newString
 -thing3
  -newString
  -newString
  -newString

In other languages, this is what I would expect to see if thing.listOfStrings was static. Is there some subtlety of python that I’m missing here?

Answer 1

listOfStrings is a class attribute. All the instances will share the same list

Instead you should add the attribute during __init__

class thing:
    def __init__(self):
        self.listOfStrings = []