How to merge multiple sets in Python with a generator expression?

Question

I want to join multiple sets that are obtained from instances of a class. Below is an example of what I am working with and what I tried. Changing the class is not an option.

class Salad:
   def __init__(self, dressing, veggies, others):
      self.dressing = dressing
      self.veggies = veggies
      self.others = others

SALADS = {
   'cesar'  : Salad('cesar',  {'lettuce', 'tomato'},  {'chicken', 'cheese'}),
   'taco'   : Salad('salsa',  {'lettuce'},            {'cheese', 'chili', 'nachos'})
}

I want OTHER_INGREDIENTS to be {'chicken', 'cheese', 'chili', 'nachos'}. So I tried:

OTHER_INGREDIENTS = sum((salad.others for salad in SALADS.values()), set())

That gives me an error "unsupported operand type(s) for +: 'set' and 'set' though. How do I do this?

I would prefer to use Python 2.7 without additional imports if possible.

L3viathan · Accepted Answer · 2018-08-29 16:36:15Z

7

You can use a set comprehension:

OTHER_INGREDIENTS = {
    element
    for salad in SALADS.values()
    for element in salad.others
}

answered Aug 29, 2018 at 16:36

L3viathan

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Dani Mesejo · Accepted Answer · 2018-08-29 16:38:49Z

6

You can use the function union from set:

OTHER_INGREDIENTS = set().union(*(salad.others for salad in SALADS.values()))

Output

{'chili', 'cheese', 'chicken', 'nachos'}

answered Aug 29, 2018 at 16:38

Dani Mesejo

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2 Comments

Catsunami Over a year ago

Thanks, this worked and, while the other answer worked too, this one had the format that best matched our repo.

Dani Mesejo Over a year ago

Glad I could help!

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