Working with Tables#

Field Properties#

List field properties of a shapefile:

fields = arcpy.ListFields("c:/shape.shp")
for field in fields:
    print(field.name, field.type, field.scale, field.precision, field.length)

Add Fields#

This function adds a field to a feature layer, shapefile, or raster file.

arcpy.AddField_management(<layer>, <field name>, <field type>, <precision>, <field scale>, <field length>)

Field Type	Description
TEXT	Names or other textual qualities
FLOAT	Numeric values with fractional values within a specific range
DOUBLE	Numeric values with fractional values within a specific range
SHORT	Numeric values without fractional values within a specific range; coded values
LONG	Numeric values without fractional values within a specific range
DATE	Date and/or time

Table Editing#

Cursors are used to access and iterate over the attribute tables of a feature class.

Cursor	Purpose
`arcpy.da.SearchCursor(in_table, field_names, {where_clause}, {spatial_reference}, {explode_to_points}, {sql_clause})`	Reading rows
`arcpy.da.UpdateCursor(in_table, field_names, {where_clause}, {spatial_reference}, {explode_to_points}, {sql_clause})`	Updating or deleting rows
`arcpy.da.InsertCursor(in_table, field_names)`	Inserting rows

Search#

with arcpy.da.SearchCursor(layer, ['fieldA', 'fieldB']) as cursor:
    for row in cursor:
        print(row[0], row[1])

Update and Delete#

with arcpy.da.UpdateCursor(layer, ["roadtype", "distance"]) as cursor:
    for row in cursor:
        row[1] = row[0] * 100
        cursor.updateRow(row)

with arcpy.da.UpdateCursor(layer, ["roadtype"]) as cursor:
    for row in cursor:
        if row[0] == 4:
            cursor.deleteRow()

Insert#

cursor = arcpy.da.InsertCursor(layer, ["roadID", "Length"])
cursor.insertRow([0, 100])

Geometries#

Token	Description
`SHAPE@`	A geometry object for the feature
`SHAPE@XY`	A tuple of the feature’s centroid x,y coordinates
`SHAPE@X`	A double of the feature’s x-coordinate
`SHAPE@AREA`	A double of the feature’s area
`SHAPE@LENGTH`	A double of the feature’s length
`SHAPE@TRUECENTROID`	A tuple of the feature’s true centroid x,y coordinates

with arcpy.da.SearchCursor(infc, ['SHAPE@XY']) as cursor:
    for row in cursor:
        x, y = row[0]

with arcpy.da.SearchCursor(infc, ['SHAPE@AREA']) as cursor:
    for row in cursor:
        area = row[0]

with arcpy.da.SearchCursor(infc, ['SHAPE@']) as cursor:
    for row in cursor:
        area = row[0].area

Count of Vertices#

shp = r'\temp\shield.shp'
features = [feature[0] for feature in arcpy.da.SearchCursor(shp, "SHAPE@")]
count_vertices = sum([f.pointCount - f.partCount for f in features])

## Alternative (slower)
polys = []
with arcpy.da.SearchCursor(shp, ["SHAPE@"]) as cursor:
    for row in cursor:
        polys.append(row[0].pointCount)
print(sum(polys))

Selection with SQL Queries#

Some functions need an SQL expression to query table attributes, such as Select_analysis (Shape Analysis), SelectLayerByAttribute (Data Management), or Extract by Attributes (Spatial Analyst).

The clause of a query must be a string with the SQL expression.

Single Clause#

in_features = "cities.shp"
out_feature_class = "cities_Class4.shp"
clause = '"CLASS" = 4'
arcpy.Select_analysis(in_features, out_feature_class, clause)

In a Loop#

in_features = "cities.shp"
for clas in ['3', '4']:
    clause = "{} = '{}'".format("FIELD", clas)
    selection = arcpy.SelectLayerByAttribute_management(in_features, "NEW_SELECTION", clause)
    arcpy.CopyFeatures_management(selection, 'cities_Class%s.shp' % (clas))

If the clause needs to change according to a variable, the string must be concatenated. Examples of SQL strings:

clause = '"CLASS" = %s' % 4               # -> '"CLASS" = 4'
clause = '"CLASS" = {}'.format(4)          # -> '"CLASS" = 4'

clause = '"NUTS" = \'%s\'' % "AT111"      # -> '"NUTS" = 'AT111''
clause = '"NUTS" = \'{}\''.format('AT111') # -> '"NUTS" = 'AT111''

clause = '"COSN5" LIKE \'%s\'' % "3.1.3%" # -> '"COSN5" LIKE '3.1.3%''
clause = '"COSN5" LIKE \'{}\''.format('3.1.3%')

clause = '"%s" = 10' % "T20"              # -> '"T20" = 10'
clause = '"{}" = 10'.format('T20')        # -> '"T20" = 10'

Raster Table#

ras_file = "majorrds.tif"
data = {row[0]: row[1] for row in arcpy.da.SearchCursor(ras_file, ['Value', 'Count'])}