UpdateCursor (arcpy.da)

Summary

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.

Discussion

Update cursors can be iterated using a for loop. Update cursors also support with statements. Using a with statement will guarantee close and release of database locks and reset iteration.

Note:

Opening simultaneous insert and/or update operations on the same workspace using different cursors requires the start of an edit session.

Note:

The Calculate Field tool provides another approach for updating field values.

Note:

arcpy.da.UpdateCursor should not be confused with the arcpy.UpdateCursor.

Syntax

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

Parameter	Explanation	Data Type
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: SHAPE@XY —A tuple of the feature's centroid x,y coordinates. SHAPE@TRUECENTROID —A tuple of the feature's true centroid x,y coordinates. SHAPE@X —A double of the feature's x-coordinate. SHAPE@Y —A double of the feature's y-coordinate. SHAPE@Z —A double of the feature's z-coordinate. SHAPE@M —A double of the feature's m-value. SHAPE@JSON — The esri JSON string representing the geometry. SHAPE@WKB —The well-known binary (WKB) representation for OGC geometry. It provides a portable representation of a geometry value as a contiguous stream of bytes. SHAPE@WKT —The well-known text (WKT) representation for OGC geometry. It provides a portable representation of a geometry value as a text string. SHAPE@ —A geometry object for the feature. SHAPE@AREA —A double of the feature's area. SHAPE@LENGTH —A double of the feature's length. OID@ —The value of the ObjectID field. Note: SHAPE@JSON, SHAPE@WKB, and SHAPE@WKT tokens were made available at ArcGIS 10.1 Service Pack 1.	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 and Specifying a query in Python. (The default value is None)	String
spatial_reference	The Spatial Reference of the feature class can be specified with either a SpatialReference object or string equivalent. (The default value is 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. (The default value is False)	Boolean
sql_clause	An optional pair of SQL prefix and postfix clauses organized in a list or tuple. SQL prefix supports None, DISTINCT, and TOP. SQL postfix 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. Note: This functionality is only available when working with geodatabases. Other data sources do not support it. (The default value is (None, None))	tuple

Properties

Property	Explanation	Data Type
fields (Read Only)	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).	tuple

Method Overview

Method	Explanation
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.

Methods

deleteRow ()

next ()

Return Value

Data Type	Explanation
tuple

reset ()

updateRow (row)

Parameter	Explanation	Data Type
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

Code Sample

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] > 20):
            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")