ArcMap

SearchCursor

Résumé

SearchCursor establishes read-only access to the records returned from a feature class or table.

Returns an iterator of tuples. The order of values in the tuple matches the order of fields specified by the field_names argument.

Discussion

Geometry properties can be accessed by specifying the token SHAPE@ in the list of fields.

Search cursors can be iterated using a for loop. Search 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.

The records returned by SearchCursor can be constrained to match attribute criteria or spatial criteria.

Accessing full geometry with SHAPE@ is an expensive operation. If only simple geometry information is required, such as the x,y coordinate of a point, use tokens such as SHAPE@XY, SHAPE@Z, and SHAPE@M for faster, more efficient access.

In Python 2, SearchCursor 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.

Syntaxe

SearchCursor
 (in_table, field_names, {where_clause}, {spatial_reference}, {explode_to_points}, {sql_clause})
ParamètreExplicationType de données
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 —Tuple des coordonnées x,y du centroïde de l'entité.
  • SHAPE@TRUECENTROID —Tuple des coordonnées x,y du centroïde réel de l'entité.
  • SHAPE@X —Double de la coordonnée x de l'entité.
  • SHAPE@Y —Double de la coordonnée y de l'entité.
  • SHAPE@Z —Double de la coordonnée z de l'entité.
  • SHAPE@M —Double de la valeur m de l'entité.
  • SHAPE@JSON — Chaîne JSON d'esri représentant la géométrie.
  • SHAPE@WKB —Représentation binaire connue (WKB) de la géométrie de l'OGC. Cette représentation constitue une représentation portable d'une valeur de géométrie sous la forme d'un flux contigu d'octets.
  • SHAPE@WKT —Représentation textuelle connue (WKT) de la géométrie de l'OGC. Cette représentation constitue une représentation portable d'une valeur de géométrie sous la forme d'une chaîne de texte.
  • SHAPE@ —Objet géométrie de l'entité.
  • SHAPE@AREA —Double de la surface de l'entité.
  • SHAPE@LENGTH —Double de la longueur de l'entité.
  • OID@ —Valeur du champ IdObjet.
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.

(La valeur par défaut est None)

String
spatial_reference

The spatial reference of the feature class. It can be specified with either a SpatialReference object or string equivalent.

(La valeur par défaut est 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.

(La valeur par défaut est 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.

(La valeur par défaut est (None, None))

tuple

Propriétés

PropriétéExplicationType de données
fields
(Lecture seule)

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

Vue d'ensemble des méthodes

MéthodeExplication
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.

Méthodes

next ()

Valeur renvoyée

Type de donnéesExplication
tuple
reset ()

Exemple de code

SearchCursor example 1

Use SearchCursor to step through a feature class and print specific field values and the x,y coordinates of the point.

import arcpy

fc = 'c:/data/base.gdb/well'
fields = ['WELL_ID', 'WELL_TYPE', 'SHAPE@XY']

# For each row print the WELL_ID and WELL_TYPE fields, and
# the feature's x,y coordinates
with arcpy.da.SearchCursor(fc, fields) as cursor:
    for row in cursor:
        print(u'{0}, {1}, {2}'.format(row[0], row[1], row[2]))
SearchCursor example 2

Use SearchCursor to return a set of unique field values.

import arcpy

fc = 'c:/data/base.gdb/well'
field = 'Diameter'

# Use SearchCursor with list comprehension to return a
# unique set of values in the specified field
values = [row[0] for row in arcpy.da.SearchCursor(fc, field)]
uniqueValues = set(values)

print(uniqueValues)
SearchCursor example 3

Use SearchCursor to return attributes using tokens.

import arcpy

fc = 'c:/data/base.gdb/well'

# For each row, print the Object ID field, and use the SHAPE@AREA
#  token to access geometry properties
with arcpy.da.SearchCursor(fc, ['OID@', 'SHAPE@AREA']) as cursor:
    for row in cursor:
        print('Feature {} has an area of {}'.format(row[0], row[1]))
SearchCursor example 4

Use SearchCursor with a where clause to identify features that meet specific criteria.

import arcpy

fc = 'c:/base/data.gdb/roads'
class_field = 'Road Class'
name_field = 'Name'

# Create an expression with proper delimiters
expression = u'{} = 2'.format(arcpy.AddFieldDelimiters(fc, name_field))

# Create a search cursor using an SQL expression
with arcpy.da.SearchCursor(fc, [class_field, name_field],
                           where_clause=expression) as cursor:
    for row in cursor:
        # Print the name of the residential road
        print(row[1])
SearchCursor example 5A

Use SearchCursor and the Python sorted method to sort rows.For additional sorting options, see the Python Sorting Mini-HOW TO.

import arcpy

fc = 'c:/data/base.gdb/well'
fields = ['WELL_ID', 'WELL_TYPE']

# Use Python's sorted method to sort rows
for row in sorted(arcpy.da.SearchCursor(fc, fields)):
    print(u'{0}, {1}'.format(row[0], row[1]))
SearchCursor example 5B

Alternatively, sort using sql_clause if the data supports SQL ORDER BY.

import arcpy

fc = 'c:/data/base.gdb/well'
fields = ['WELL_ID', 'WELL_TYPE']

# Use ORDER BY sql clause to sort field values
for row in arcpy.da.SearchCursor(
        fc, fields, sql_clause=(None, 'ORDER BY WELL_ID, WELL_TYPE')):
    print(u'{0}, {1}'.format(row[0], row[1]))
SearchCursor example 6

Use SQL TOP to limit the number of records to return.

import arcpy

fc = 'c:/data/base.mdb/well'
fields = ['WELL_ID', 'WELL_TYPE']

# Use SQL TOP to sort field values
for row in arcpy.da.SearchCursor(fc, fields, sql_clause=('TOP 3', None)):
    print(u'{0}, {1}'.format(row[0], row[1]))

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