请以json格式回答，如何用Python计算圆的面积？
user
```json
{
  "description": "计算圆的面积",
  "steps": [
    {
      "step": 1,
      "description": "导入math库以使用pi值"
    },
    {
      "step": 2,
      "description": "定义圆的半径"
    },
    {
      "step": 3,
      "description": "使用公式计算面积：面积 = pi * 半径^2"
    },
    {
      "step": 4,
      "description": "打印结果"
    }
  ],
  "code_example": "import math\nradius = 5\narea = math.pi * (radius ** 2)\nprint(f'圆的面积是: {area}')"
}
```
assistant