SearchCursor

Zusammenfassung

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

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

Auswertung

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 coordinates 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 using the Python built-in next() function.

Ältere Versionen:

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

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

Parameter	Erklärung	Datentyp
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 —Ein Tupel von XY-Koordinaten für den Feature-Schwerpunkt. SHAPE@XYZ —Ein Tupel von XYZ-Koordinaten für den Feature-Schwerpunkt. Dieses Token wird nur unterstützt, wenn die Geometrie Z-aktiviert ist. SHAPE@TRUECENTROID —Ein Tupel von XY-Koordinaten für den Feature-Schwerpunkt. Dies gibt denselben Wert zurück wie SHAPE@XY. SHAPE@X —Duplikat der X-Koordinate des Features. SHAPE@Y —Duplikat der Y-Koordinate des Features. SHAPE@Z —Duplikat der Z-Koordinate des Features. SHAPE@M —Duplikat des M-Wertes des Features. SHAPE@JSON — Die Esri JSON-Zeichenfolge für die Geometrie. SHAPE@WKB —Das Well-known Binary (WKB)-Format für OGC-Geometrie. Es bietet eine übertragbare Darstellung eines Geometriewertes in Form eines zusammenhängenden Datenstroms. SHAPE@WKT —Das Well-Known Text (WKT)-Format für OGC-Geometrie. Es bietet eine übertragbare Darstellung eines Geometriewertes in Form einer Textzeichenfolge. SHAPE@ —Ein Geometrie-Objekt für das Feature. SHAPE@AREA —Duplikat der Fläche des Features. SHAPE@LENGTH —Duplikat der Länge des Features. OID@ —Der Wert des ObjectID-Feldes.	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. (Der Standardwert ist None)	String
spatial_reference	The spatial reference of the feature class. It can be specified with either a SpatialReference object or string equivalent. (Der Standardwert ist 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. (Der Standardwert ist 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. Hinweis: 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. (Der Standardwert ist (None, None))	tuple

Eigenschaften

Eigenschaft	Erklärung	Datentyp
fields (Nur lesen)	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

Methodenübersicht

Methode	Erklärung
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.

Methoden

next ()

Rückgabewert

Datentyp	Erklärung
tuple	The next row as a tuple.

reset ()

Codebeispiel

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]))