5.16 Best Practices

Readability

Choose the type whose name and behavior best communicate intent — a set clearly signals “uniqueness matters here” in a way a list doesn’t, even if a list would technically also work.

Consistency

Don’t let a variable silently change type across a function’s logic (see 5.15 Common Mistakes) — if a value starts as an int, keep it an int unless converting is the explicit point of that line.

Efficient Data Structures

Default to list for an ordered, changing collection; reach for set or dict when uniqueness or fast lookup is the actual requirement — revisit 5.13 Choosing the Right Data Type’s performance guidance when a script feels slower than it should.

Quick Interview Answer

“Good data-type practice comes down to three habits: pick the type that communicates intent (a set says ‘uniqueness matters’ more clearly than a list), keep a variable’s type consistent within a function’s logic rather than letting it silently drift, and default to list for ordered collections but reach for set/dict specifically when uniqueness or fast lookup is the real requirement.”

Common Mistakes

• Using a list everywhere out of habit, even in cases where a set or dict would communicate intent and perform better.
• Letting a variable’s type change mid-function without a clear, intentional conversion step.