loop_thru_layer_and_clip.py

# ---------------------------------------------------------------------------
# Name: Loop Through Layer "A" and Clip Features from Layer "B"
#
# Author: Patrick McKinney, Cumberland County GIS (pmckinney@ccpa.net or pnmcartography@gmail.com)
#
# Created on: 6/21/2019
#
# Description: This sample script provides a template for how to loop through a layer (A) and clip features
# from another layer (B) based upon each record in layer A.
#
# As an example, you may want to clip a hydrography layer by each County in a state.  This script
# automates what would otherwise be a long manual process.
#
# Disclaimer: CUMBERLAND COUNTY ASSUMES NO LIABILITY ARISING FROM USE OF THESE MAPS OR DATA. THE MAPS AND DATA ARE PROVIDED WITHOUT
# WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
# FITNESS FOR A PARTICULAR PURPOSE.
# Furthermore, Cumberland County assumes no liability for any errors, omissions, or inaccuracies in the information provided regardless
# of the cause of such, or for any decision made, action taken, or action not taken by the user in reliance upon any maps or data provided
# herein. The user assumes the risk that the information may not be accurate.
# ---------------------------------------------------------------------------

# Import system modules
import arcpy, sys, os

# Run geoprocessing tool.
# If there is an error with the tool, it will break and run the code within the except statement
try:
    # location where you want the clipped layers to be stored
    out_gdb = r'C:\GIS\Clipped\Output.gdb'
    # Geodatabase storing layers that participate in clip
    # you can also reference the full path to each layer when you construct its variable
    parent_gdb = r'G:\Data\Geodata.gdb'
    # hydrography (streams) layer
    streams_fc = os.path.join(parent_gdb, 'Streams_Polyline')
    # counties layer
    counties = os.path.join(parent_gdb, 'Counties')
    # fields from Counties layer to use in cursor
    county_fields = ['OBJECTID','NAME']
    # create feature layer for Counties so you can clip by each record within cursor
    arcpy.MakeFeatureLayer_management(counties,'County')
    # print statement to console
    print 'Created feature layer for Counties layer\n'

    # Create Search Cursor for Counties
    # print statement to console
    print '\nCreating search cursor on Counties layer'
    # create search cursor
    with arcpy.da.SearchCursor(counties, county_fields) as cursor:
        # loop through each record in Counties layer
        for row in cursor:
            # where clause
            where_clause = "OBJECTID = {}".format(row[0])
            # select the current record from the Counties layer using OBJECTID
            arcpy.SelectLayerByAttribute_management('County', 'NEW_SELECTION', where_clause)
            # clip streams by county
            arcpy.Clip_analysis(streams_fc, 'County', os.path.join(out_gdb, '{}_Streams'.format(row[1])))
            # print statement to console
            print 'Clipped Streams layer for {}\n'.format(row[1])
        # end for
    # end with cursor
    
    # delete cursor
    del cursor
# If an error occurs running geoprocessing tool(s) capture error and write message
# handle error outside of Python system
except EnvironmentError as e:
    tbE = sys.exc_info()[2]
    # add the line number the error occured to the log message
    print "Failed at Line {}\n".format(tbE.tb_lineno)
    # add the error message to the log message
    print "Error: {}\n".format(str(e))
# handle exception error
except Exception as e:
    # Store information about the error
    tbE = sys.exc_info()[2]
    # add the line number the error occured to the log message
    print "Failed at Line {}\n".format(tbE.tb_lineno)
    # add the error message to the log message
    print "Error: {}\n".format(e.message)