# ValueError: 等高线级别数必须至少为2，但得到了1。

- **ID:** `python/matplotlib-contour-levels-error`
- **领域:** python
- **类别:** runtime_error
- **验证级别:** ai_generated
- **修复率:** 80%

## 根因

向contour/contourf的levels参数传递了单个值，但绘制等高线至少需要两个级别。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| 3.7 | active | — | — |
| 3.8 | active | — | — |

## 解决方案

1. **Provide at least two levels as an array** (95% 成功率)
   ```
   plt.contour(X, Y, Z, levels=[0, 1, 2])
   ```
2. **Use an integer to specify the number of automatically chosen levels** (90% 成功率)
   ```
   plt.contour(X, Y, Z, levels=10)  # at least 2
   ```

## 无效尝试

- **Using a negative number of levels** — Levels must be positive integers or an array; negative numbers raise a different error. (90% 失败率)
- **Setting levels as a string like 'auto'** — In some versions, 'auto' is not a valid input; it must be a number or array. (70% 失败率)