# 2.3.shapefile更新

更新shapefile使用的是`arcpy.da.UpdateCursor`函数，UpdateCursor 能够对游标所访问的数据进行读写，其定义如下：

```
UpdateCursor(in_table, field_names, {where_clause}, {spatial_reference}, {explode_to_points}, {sql_clause})
```

参数的意义与`arcpy.da.SearchCursor`相同。

> `UpdateCursor`具有四个方法：
>
> `deleteRow()`：删除当前要素
>
> `next()`：用于迭代时获取下一行数据
>
> `reset()`：将游标重置到第一行
>
> `updateRow(row)`：更新当前行数据

接下来来看一段代码：

```
shp_file_path = ur'../data/ReadData/Point.shp'
fields_array = ['SHAPE@', 'Id']
# 定义WGS84坐标系
spatial_reference = arcpy.SpatialReference(4326)
with arcpy.da.UpdateCursor(shp_file_path, fields_array, spatial_reference=spatial_reference) as cursor:
    row_index = 0
    for row in cursor:
        if row_index == 0:
            new_id = random.randint(1, 100)
            row[1] = new_id
        else:
            new_y = random.randint(-90, 90)
            old_pt = row[0].firstPoint
            row[0] = arcpy.Point(old_pt.X, new_y)
        row_index += 1
        cursor.updateRow(row)
```

这段代码是更新了一个“Point.shp”文件。开始，我们定义了需要搜索的字段为\['SHAPE@', 'Id']，当`row_index == 0`时，更改了属性中的第2个字段——Id——为一个随机整数；当`row_index == 1`时，更改了属性中的第1个字段——几何信息，此处为点——的y坐标为一个在\[-90,90]之间的随机整数。

注意：根据图层类型的不同，当更新几何信息时，所构建的几何对象也不同，这一点和添加要素时是一致的，具体请看上一节。


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