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.

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:

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

Note:

Using UpdateCursor on versioned data requires the start of an edit session.

Note:

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

Legacy:

The arcpy.da cursors (arcpy.da.SearchCursor, arcpy.da.UpdateCursor, and arcpy.da.InsertCursor) were introduced with ArcGIS 10.1 to provide significantly faster performance over the previously existing set of cursor functions (arcpy.SearchCursor, arcpy.UpdateCursor, and arcpy.InsertCursor). The original cursors are provided only for continuing backward compatibility.

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.	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. (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: 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 and MS Access databases. (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). The order of the field names on the fields property will be the same as passed in with the field_names argument.	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	The next row as a 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] > 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')