Set operations

Combine two or more collections into a single set of unique elements.

Data processing: merging tag lists from multiple sources; Access control: combining permission sets for a user; Analytics: aggregating unique identifiers across datasets

Python standard library, data processing, algorithms, any code needing set semantics.

base_set.union(additional_items)

... .union(...)

base_set: set of hashable items; additional_items: iterable of hashable items (e.g., list, set, tuple)

• set.intersection
• set.difference
• set.update
• set.symmetric_difference

• base_set | additional_items (using union operator)

Assuming union modifies the original set; passing non‑hashable items; forgetting that union returns a new set.

set.update() – modifies the set in place; set.union() – returns a new set.

Coming from SQL: expecting UNION to modify the original table; in Python union returns a new set and leaves operands unchanged.

• set.intersection
• set.difference
• set.symmetric_difference
• set.update

Accepts any iterable; duplicates are removed; result is a new set; if you need in‑place merging, use update().

Enables functional, side‑effect‑free code; avoids accidental mutation of original collections.

Think of a union as a set wedding – bringing together two families without changing either family.

The union operation returns a new set; original sets remain unchanged. Use the union operator | for concise syntax when both operands are sets.

Using set.update() for in‑place union, or functools.reduce with union for many sets.