UpdateCursor

Résumé

UpdateCursor établit un accès en lecture et en écriture aux enregistrements renvoyés par une classe d'entités ou une table.

Renvoie un itérateur de listes. L'ordre des valeurs dans la liste correspond à l'ordre des champs spécifiés par l'argument field_names.

Discussion

Une boucle for peut être utilisée pour itérer les curseurs de mise à jour. Les curseurs de mise à jour prennent également en charge les instructions with pour réinitialiser l'itération et aider à supprimer les verrouillages. Toutefois, l'utilisation d'une instruction del pour supprimer l'objet ou renvoyer le curseur dans une fonction afin de mettre l'objet curseur hors de portée doit être pris en compte afin de prévenir tout cas de verrouillage.

Dans Python 2, UpdateCursor prend en charge la méthode next d'itérateur pour récupérer la prochaine ligne d'une boucle. Dans Python 3, ceci est effectué à l'aide de la fonction Python next intégrée.

Remarque :

Ouvrir simultanément des opérations d'insertion et de mise à jour dans le même espace de travail à l'aide de différents curseurs requiert l'ouverture d'une session de mise à jour.

Remarque :

L'utilisation de UpdateCursor sur des données versionnées nécessite le lancement d'une session de mise à jour.

Remarque :

Les outils Calculate Field (Calculer un champ) et Calculate Fields (Calculer des champs) peuvent aussi être utilisés pour mettre à jour les valeurs des champs.

Syntaxe

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

Paramètre	Explication	Type 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 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@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. 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. (La valeur par défaut est 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. (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. 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. Remarque : 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. (La valeur par défaut est (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

Propriétés

Propriété	Explication	Type 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

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

Méthodes

deleteRow ()

reset ()

updateRow (row)

Paramètre	Explication	Type de données
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

Exemple de code

Exemple 1 d'utilisation de la fonction UpdateCursor

Utilisez UpdateCursor pour mettre à jour la valeur d'un champ en évaluant les valeurs d'autres champs.

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)

Exemple 2 d'utilisation de la fonction UpdateCursor

Utilisez UpdateCursor pour mettre à jour un champ de distances de la zone tampon pour l'utiliser avec l'outil Buffer (Tampon).

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')