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Set Membership

Zero-dependency Python snippets for checking membership in sets using the standard library.

3 snippets available in this sub-category.

Simple

Check if item is in set

set membership in contains data-structures

Check if an element exists in a set

fruits = {"apple", "banana", "cherry"}
print("banana" in fruits)  # True
print("orange" in fruits)  # False

Notes

  • Membership checks are O(1) on average
  • Much faster than checking in a list for large collections

Not in set

set not-in membership data-structures

Check if an element does not exist in a set

numbers = {1, 2, 3}
print(4 not in numbers)  # True

Notes

  • Use not in for negative membership

Complex

Set membership with custom objects

set membership custom object hash data-structures

Check membership for custom objects in a set

class User:
    def __init__(self, name):
        self.name = name

    def __hash__(self):
        return hash(self.name)

    def __eq__(self, other):
        return isinstance(other, User) and self.name == other.name


users = {User("alice"), User("bob")}
print(User("alice") in users)  # True
print(User("carol") in users)  # False

Notes

  • Custom objects must implement hash and eq for set membership
  • Useful for deduplication of custom types

🔗 Cross Reference

🏷️ Tags

set, membership, in, not-in, custom, data-structures

📝 Notes

  • Use in and not in for fast membership checks
  • Sets are ideal for large membership tests