MediumContext ManagementPython 3
Context Window Packer
Select system and recent conversation messages without exceeding a token budget.
30m3 sample tests6 hidden tests
Choose which chat messages fit into a bounded context window.
Requirements
- Define
pack_messages(messages, max_tokens). - Each message is a dict with
id,role, andtokens. - Return the selected message IDs in original order.
- Keep the first system message if it fits.
- Ignore every later system message, even when the first system message exceeds the token budget.
- Fill the remaining budget by scanning every non-system message from newest to oldest, rather than requiring a contiguous newest suffix.
- Skip any message that doesn't fit and keep scanning older ones.
- Never exceed
max_tokens.
Example
python
1messages = [
2 {"id": "sys", "role": "system", "tokens": 2},
3 {"id": "old", "role": "user", "tokens": 3},
4 {"id": "new", "role": "assistant", "tokens": 4},
5]
6assert pack_messages(messages, 6) == ["sys", "new"]
7
8messages = [
9 {"id": "older", "role": "user", "tokens": 2},
10 {"id": "oversized", "role": "assistant", "tokens": 8},
11 {"id": "newest", "role": "user", "tokens": 2},
12]
13assert pack_messages(messages, 4) == ["older", "newest"]Constraints
- Preserve conversation order in the returned IDs.
- Prefer recency for non-system messages.
- Don't mutate the input messages.
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