UpdateCursor

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 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.

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

The following includes some dataset types that can only be edited within an edit session:

• Feature classes participating in a topology
• Feature classes participating in a geometric network
• Feature classes participating in a network dataset
• Versioned datasets in enterprise geodatabases
• Some object and feature classes with class extensions

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.

Note:

The Calculate Field and Calculate Fields tools can also be used to update field values.

Note:

Using an UpdateCursor on a layer with a joined table is not supported.

Syntax

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

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 to access all fields from the input table (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@XYZ—A tuple of the feature's centroid x,y,z coordinates. SHAPE@TRUECENTROID—A tuple of the feature's centroid x,y coordinates. This returns the same value as SHAPE@XY. 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. Values are returned as a bytearray object, but can be updated as a bytearray or bytes object. 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 Object ID field.	String
where_clause	An optional expression that limits the records returned. For more information on where clauses and SQL statements, see SQL reference for query expressions used in ArcGIS. (The default value is None)	String
spatial_reference	The spatial reference of the feature class. When this argument is specified, the feature will be projected (or transformed) from the input's spatial reference. If unspecified, the input feature classes' spatial reference will be used. Valid values for this argument are 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	A 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. Use DISTINCT in a prefix clause. with arcpy.da.UpdateCursor( in_features, ["OID@", "STREET_NAME"], sql_clause=("DISTINCT STREET_NAME", None) ) as cur: Use TOP in a prefix clause, and ORDER BY in a postfix clause. with arcpy.da.UpdateCursor( in_features, ['OID@', "ELEVATION"], sql_clause=("TOP 5", "ORDER BY ELEVATION DESC") ) as cur: Use GROUP BY in a postfix clause. with arcpy.da.UpdateCursor( in_features, ['STREET_NAME'], sql_clause=(None, "GROUP BY STREET_NAME") ) as cur: 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: DISTINCT, ORDER BY, and ALL are only supported when working with databases. They are not supported by other data sources (such as dBASE or INFO tables). TOP is only supported by SQL Server databases. (The default value is (None, None))	tuple
datum_transformation	When the cursor projects the features from one spatial reference to another, if the spatial references do not share the same datum, an appropriate datum transformation should be specified. An update cursor can perform a projection or transformation at two stages: when reading the features from the feature class on disk, and when writing the updated features into the feature class. The ListTransformations function can be used to provide a list of valid datum transformations between two spatial references. Learn more about datum transformations	String

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. The order of the field names on the fields property will be the same as passed in with the field_names argument. If the field_names argument is set to *, the fields property will include all fields used by the cursor. A value of * will return geometry in a tuple of x,y coordinates (equivalent to the SHAPE@XY token).	tuple

Method Overview

Method	Explanation
deleteRow ()	Deletes the current row.
reset ()	Resets the cursor back to the first row.
updateRow (row)	Updates the current row in the table.

Methods

deleteRow ()

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] > 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 function.

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')