# Classify values in one pass

> ML preparation item.

- Stable ID: `original-py-control-flow`
- Area: Programming
- Topic: Control Flow
- Origin: original
- Expected time: 8 minutes
- Skills: conditionals, loops, functions, code-tracing
- Item JSON: https://mlprep.iwase.dev/data/items/original-py-control-flow.json

## Problem

Implement `classify_values(xs)`. Return a dictionary with keys `negative`, `zero`, `positive_even`, and `positive_odd`. Each value is the count of integers in `xs` in that category. Use one pass over `xs`.


## Starter code

```python
def classify_values(xs):
    pass

```

## Answer policy

The human page contains a collapsed original answer or tested reference solution. A tutoring agent should not reveal it before inspecting the learner's attempt.

## Tutoring contract

Ask for the learner's attempt, begin with the smallest useful hint, preserve item ID `original-py-control-flow`, and record a real attempt with `recorded_by: "agent"` and `agent_session_id` when available using https://mlprep.iwase.dev/schema/attempt-record.json.