Today I'm reading about sets. I knew a few things about sets:
- Sets are mutable, unordered, collections of unique objects
- You can declare an empty set with 'set()'
- You can declare a set with things in it like this: '{1, 2, 2}'
- You can get the difference, union, intersection, etc. like this:
- my_set.thing_I_want(other_set)
- How to create a set comprehension
But there were things I didn't know about sets:
- You don't have to use the .operation() version, you can use operators! Some of which are more intuitive to me than others.
| Operation | Equivalent | Result |
|---|---|---|
| s.issubset(t) | s <= t | test whether every element in s is in t |
| s.issuperset(t) | s >= t | test whether every element in t is in s |
| s.union(t) | s | t | new set with elements from both s and t |
| s.intersection(t) | s & t | new set with elements common to s and t |
| s.difference(t) | s - t | new set with elements in s but not in t |
| s.symmetric_difference(t) | s ^ t | new set with elements in either s or t but not both |
| s.update(t) | s |= t | return set s with elements added from t |
| s.intersection_update(t) | s &= t | return set s keeping only elements also found in t |
| s.difference_update(t) | s -= t | return set s after removing elements found in t |
| s.symmetric_difference_update(t) | s ^= t | return set s with elements from s or t but not both |
- There is such a thing as immutable set (it's another class)*
- If you do use the operation_name function version for union, intersection, difference, or symmetric_difference, you don't need to cast the second thing to a set (it just needs to be iterable)
*Edited to add that I've realised it's depreciated and replaced by frozenset since 2.6
