Resumen
The UpdateCursor function creates a cursor that allows you to update or delete rows on the specified feature class, shapefile, or table. The cursor places a lock on the data that will remain until either the script completes or the update cursor object is deleted.
Debate
Update cursors can be iterated with a for loop or in a while loop using the cursor's next method to return the next row. When using the next method on a cursor to retrieve all rows in a table containing N rows, the script must make N calls to next. A call to next after the last row in the result set has been retrieved returns None, which is a Python data type that acts here as a placeholder.
Using UpdateCursor with a for loop.
import arcpy
fc = "c:/data/base.gdb/roads"
field1 = "field1"
field2 = "field2"
cursor = arcpy.UpdateCursor(fc)
for row in cursor:
# field2 will be equal to field1 multiplied by 3.0
row.setValue(field2, row.getValue(field1) * 3.0)
cursor.updateRow(row)
Using UpdateCursor with a while loop.
import arcpy
fc = "c:/data/base.gdb/roads"
field1 = "field1"
field2 = "field2"
cursor = arcpy.UpdateCursor(fc)
row = cursor.next()
while row:
# field2 will be equal to field1 multiplied by 3.0
row.setValue(field2, row.getValue(field1) * 3.0)
cursor.updateRow(row)
row = cursor.next()
Sintaxis
UpdateCursor (dataset, {where_clause}, {spatial_reference}, {fields}, {sort_fields})
Parámetro | Explicación | Tipo de datos |
dataset | The feature class, shapefile, or table containing the rows to be updated or deleted. | String |
where_clause | An optional expression that limits the rows returned in the cursor. For more information on where clauses and SQL statements, see Building a query expression. | String |
spatial_reference | Coordinates are specified in the spatial_reference provided and converted on the fly to the coordinate system of the dataset. | SpatialReference |
fields | A semicolon-delimited string of fields to be included in the cursor. By default, all fields are included. | String |
sort_fields | The fields used to sort the rows in the cursor. Ascending and descending order for each field is denoted by A for ascending and D descending, using the form "field1 A;field2 B". | String |
Valor de retorno
Tipo de datos | Explicación |
Cursor | A Cursor object that can distribute Row objects. |
Muestra de código
UpdateCursor example
Update field values in a feature class based on another field's value.
import arcpy
# Create update cursor for feature class
rows = arcpy.UpdateCursor("c:/data/base.gdb/roads")
# Update the field used in buffer so the distance is based on the
# road type. Road type is either 1, 2, 3, or 4. Distance is in meters.
for row in rows:
# Fields from the table can be dynamically accessed from the
# row object. Here fields named BUFFER_DISTANCE and ROAD_TYPE
# are used
row.setValue("BUFFER_DISTANCE", row.getValue("ROAD_TYPE") * 100)
rows.updateRow(row)
# Delete cursor and row objects to remove locks on the data.
del row
del rows