COMP 110 JUNE 2-6

Why avoid in with large lists?

Must scan every item (slow for big lists).

Lists allow duplicates?

Yes.

Lists maintain order?

Yes, by index (0, 1, 2...).

Sets allow duplicates?

No, auto-removed.

How to add to a set?

my_set.add(item).

Empty set syntax?

set() (not {}).

Why use sets over lists?

Faster membership checks.

How to add/update a key-value pair?

my_dict["key"] = value.

What happens to duplicate keys?

Last value wins ({"a":1, "a":2} → {"a":2}).

Safe way to check keys?

"key" in my_dict or .get(key, default).

How to remove a key?

.pop(key) or del my_dict["key"].

Dictionary keys changeable?

No (must be strings, numbers, tuples).

Empty dict syntax?

{} or dict().

How to loop key-value pairs?

for key, value in my_dict.items():.

{1,2,2} becomes?

{1,2}.

len({"a":1, "b":2})?

2

What does for x in my_dict: loop over?

The keys (use my_dict[x] to get values).

Error for missing keys?

KeyError (use .get() to avoid).

pop() missing key?

Raises KeyError (add default: .pop(key, None)).

What does "zero-based" mean for lists?

First item is at index 0 (not 1).

How are lists sequential?

Items keep their order (index 0 → 1 → 2...).