---
id: 530bfb6f-841c-4381-b8a4-d0b6fbc02878
type: fix
title: "Fix: Pydantic bare default evaluated at class definition time (paper-dynasty-database)"
tags: [paper-dynasty, python, pydantic, fix, bug, fastapi]
importance: 0.65
confidence: 0.8
created: "2026-03-03T20:06:06.122074+00:00"
updated: "2026-03-03T20:06:06.763300+00:00"
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---

## Problem

`PlayerModel.offense_col` in `app/routers_v2/mlbplayers.py` used a bare `random.randint(1, 3)` as the Pydantic field default. Python evaluates this expression once at class definition time (module import), so every instance shared the same random integer for the entire process lifetime.

## Root Cause

Pydantic field defaults that are not wrapped in `Field(default_factory=...)` are evaluated eagerly at class body execution time — identical to how Python function default argument values work. This is a common footgun with mutable or randomised defaults.

## Solution

```python
# Before (broken)
offense_col: int = random.randint(1, 3)

# After (correct)
offense_col: int = pydantic.Field(default_factory=lambda: random.randint(1, 3))
```

`default_factory` is called on each model instantiation, producing a fresh value per request.

## Files Changed

- `app/routers_v2/mlbplayers.py` line 40

## References

- Issue #24, PR #38 in cal/paper-dynasty-database