概要
UpdateCursor establishes read-write access to records returned from a feature class or table.
Returns an iterator of lists. The order of values in the list matches the order of fields specified by the field_names argument.
ディスカッション
Update cursors can be iterated using a for loop. Update cursors also support with statements to reset iteration and aid in removal of locks. However, using a del statement to delete the object or wrapping the cursor in a function to have the cursor object go out of scope should be considered to guard against all locking cases.
In Python 2, UpdateCursor supports the iterator .next() method to retrieve the next row outside of a loop. In Python 3, the equivalent is performed by using the Python built-in next() function.
構文
UpdateCursor (in_table, field_names, {where_clause}, {spatial_reference}, {explode_to_points}, {sql_clause})| パラメーター | 説明 | データ タイプ |
in_table | The feature class, layer, table, or table view. | String |
field_names [field_names,...] | A list (or tuple) of field names. For a single field, you can use a string instead of a list of strings. Use an asterisk (*) instead of a list of fields if you want to access all fields from the input table (raster and BLOB fields are excluded). However, for faster performance and reliable field order, it is recommended that the list of fields be narrowed to only those that are actually needed. Raster fields are not supported. Additional information can be accessed using tokens (such as OID@) in place of field names:
| String |
where_clause | An optional expression that limits the records returned. For more information on WHERE clauses and SQL statements, see Building a query expression. (デフォルト値は次のとおりです None) | String |
spatial_reference | The spatial reference of the feature class can be specified with either a SpatialReference object or string equivalent. (デフォルト値は次のとおりです None) | SpatialReference |
explode_to_points | Deconstruct a feature into its individual points or vertices. If explode_to_points is set to True, a multipoint feature with five points, for example, is represented by five rows. (デフォルト値は次のとおりです False) | Boolean |
sql_clause | An optional pair of SQL prefix and postfix clauses organized in a list or tuple. An SQL prefix clause supports None, DISTINCT, and TOP. An SQL postfix clause supports None, ORDER BY, and GROUP BY. An SQL prefix clause is positioned in the first position and will be inserted between the SELECT keyword and the SELECT COLUMN LIST. The SQL prefix clause is most commonly used for clauses such as DISTINCT or ALL. An SQL postfix clause is positioned in the second position and will be appended to the SELECT statement, following the where clause. The SQL postfix clause is most commonly used for clauses such as ORDER BY. (デフォルト値は次のとおりです (None, None)) | tuple |
プロパティ
| プロパティ | 説明 | データ タイプ |
| fields (読み取り専用) | A tuple of field names used by the cursor. The tuple will include all fields (and tokens) specified by the field_names argument. If the field_names argument is set to *, the fields property will include all fields used by the cursor. When using *, geometry values will be returned in a tuple of the x,y-coordinates (equivalent to the SHAPE@XY token). The order of the field names on the fields property will be the same as passed in with the field_names argument. | tuple |
手法の概要
| 手法 | 説明 |
| deleteRow () | Deletes the current row. |
| next () | Returns the next row as a tuple. The order of fields will be returned in the order they were specified when creating the cursor. |
| reset () | Resets the cursor back to the first row. |
| updateRow (row) | Updates the current row in the table. |
手法
deleteRow ()
next ()
戻り値
| データ タイプ | 説明 |
| tuple | The next row as a tuple. |
reset ()
updateRow (row)
| パラメーター | 説明 | データ タイプ |
row | A list or tuple of values. The order of values should be in the same order as the fields. When updating fields, if the incoming values match the type of field, the values will be cast as necessary. For example, a value of 1.0 to a string field will be added as "1.0", and a value of "25" added to a float field will be added as 25.0. | tuple |
コードのサンプル
UpdateCursor example 1
Use UpdateCursor to update a field value by evaluating the values of other fields.
import arcpy
fc = 'c:/data/base.gdb/well'
fields = ['WELL_YIELD', 'WELL_CLASS']
# Create update cursor for feature class
with arcpy.da.UpdateCursor(fc, fields) as cursor:
# For each row, evaluate the WELL_YIELD value (index position
# of 0), and update WELL_CLASS (index position of 1)
for row in cursor:
if (row[0] >= 0 and row[0] <= 10):
row[1] = 1
elif (row[0] > 10 and row[0] <= 20):
row[1] = 2
elif (row[0] > 20 and row[0] <= 30):
row[1] = 3
elif (row[0] > 30):
row[1] = 4
# Update the cursor with the updated list
cursor.updateRow(row)
UpdateCursor example 2
Use UpdateCursor to update a field of buffer distances for use with the Buffer tool.
import arcpy
arcpy.env.workspace = 'c:/data/output.gdb'
fc = 'c:/data/base.gdb/roads'
fields = ['ROAD_TYPE', 'BUFFER_DISTANCE']
# Create update cursor for feature class
with arcpy.da.UpdateCursor(fc, fields) as cursor:
# Update the field used in Buffer so the distance is based on road
# type. Road type is either 1, 2, 3, or 4. Distance is in meters.
for row in cursor:
# Update the BUFFER_DISTANCE field to be 100 times the
# ROAD_TYPE field.
row[1] = row[0] * 100
cursor.updateRow(row)
# Buffer feature class using updated field values
arcpy.Buffer_analysis(fc, 'roads_buffer', 'BUFFER_DISTANCE')