Derek J. Nelson

Python: Beyond the Basics

Topics Covered

• Cursors

• Geometry objects

• Leveraging other Python modules

• Used to:

- Iterate over the set of rows in a table

- Insert new rows into a table

• Two varieties:

- arcpy.da cursors (10.1 onwards; significantly faster performance)

- “Classic” cursors (provided only for continuing backward compatibility)

Cursors

Data Access Module Cursors

• Table

- The feature class, layer, table, or table view

• Fields

- Single field or list of field names

- Index position in fields parameter defines value access

# 0 1 2

fields = [“Name”, “Year”, “Count”]

Required Arguments

Used as shortcuts in place of field names

Tokens

• OID@ —The value of the ObjectID field.

• SHAPE@ —A geometry object for the feature.

• SHAPE@XY —A tuple of the feature's centroid x,y

coordinates.

• SHAPE@TRUECENTROID —A tuple of the feature's

true centroid x,y coordinates.

• 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@AREA —A double of the feature's area.

• SHAPE@LENGTH —A double of the feature's length.

arcpy.da.SearchCursor

arcpy.da.SearchCursor(in_table, field_names, {where_clause},

{spatial_reference}, {explode_to_points}, {sql_clause})

arcpy.da.SearchCursor – optional where clause

parameter

# Open a Search Cursor, print results

table = "Crime_Incidents_2016"

fields = ["Shift", "Offense", "Method", "Ward"]

qry = " Ward = '6' "

with arcpy.da.SearchCursor(table, fields, qry) as cursor:

for row in cursor:

print("Shift: {} Offense:{} Method: {} Ward: {}".format(row[0], row[1], row[2], row[3]))

Demo: Search

Cursor and Email

Update

arcpy.da.UpdateCursor

arcpy.da.UpdateCursor(in_table, field_names, {where_clause},

{spatial_reference}, {explode_to_points}, {sql_clause})

Method Explanation

deleteRow () Deletes the current row

updateRow (row) Updates the current row in the table.

arcpy.da.UpdateCursor

arcpy.da.UpdateCursor

arcpy.da.UpdateCursor

arcpy.da.InsertCursor

arcpy.da.InsertCursor(in_table, field_names)

Method Explanation

insertRow (row) Inserts a row into a table.

arcpy.da.InsertCursor

Working with Geometry Objects

• Reading geometries

- arcpy.da.SearchCursor

- arcpy.da.UpdateCursor

• Writing geometries

- arcpy.da.UpdateCursor

- arcpy.da.InsertCursor

• Work with geoprocessing tools

Using geometry as input with geoprocessing tools

Demo: Cursor to

Collector

Leveraging other Python modules

Installed with ArcGIS Pro

• Examples:

• arcgis

• scipy

• pandas

The Python Standard Library

• Examples:

• os

• urllib

• zipfile

Additional third-party Python

packages

• Examples:

• beautifulsoup

• tensorflow

• scikit-learn

Leveraging other Python modules

• Python Standard Library

- Read a csv with the csv module

- Unzip a .zip file with the zipfile module

- Download data from the internet with the urllib module

- Automatically open an output with the os module

- … many more

• Can install other pre-existing Python packages with ArcGIS Pro Python

Package Manager

Demo: Python

Package Manager

Create and Prep

Jesse Parker

Why did we build this?

❖Show enterprise GIS data from internal network to remote clients

❖Could not change/interrupt current data editing workflow/databases

❖Saves hours of manual project setup work and reduces human error

Recommendations❖ Documentation

❖ Always reference docs paying special attention to arguments (types) and returns

❖ Learn and use a proper IDE

❖ Autocomplete, debugging, refactoring, referencing, environments, version control

❖ Variable/function/class naming, comments

❖ It does not hurt to anything to use names that make sense and makes your code readable

❖ Comments should help the reader understand the logic

❖ Use PEP 8 (Style guide) (A good IDE will help with this)

❖ Python 3

❖ ArcPro/Enterprise required to use arcpy in python 3

❖ Use ArcPro as virtual environment manager

❖ Typing! (available in python 3)

❖ function/method return types

❖ Argument types

❖ Logging

❖ Use python logging and add filter to send messages to ArcPro

Questions?

Jesse Parker

jparker@geocgi.com

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Python Sessions at FedGIS

Session Tuesday Wednesday

Python: An Introduction 1:45 pm – 2:45 pm in 146B 11:00 am – 12:00 pm in 146B

Python: Beyond the Basics 4:15 pm – 5:15 pm in 146B 1:30 pm – 2:30 pm in 146B

ArcGIS Pro: Analysis and Geoprocessing Overview 11:00 am – 12:00 pm in 147A

Python: Building Geoprocessing Tools 4:00 pm – 5:00 pm in 147B

Python: Map Automation in ArcGIS Pro 5:15 pm – 6:15 pm in 102A

Data Science in ArcGIS Using Python and R 1:45 pm – 2:45 pm in 150A 5:15 pm – 6:15 pm in 147B

Data Science Using ArcGIS Notebooks 3:00 pm – 4:00 pm in 150A 2:45 pm – 3:45 pm in 147B

Machine Learning in ArcGIS 3:00 pm – 4:00 pm in 146C 8:30 am – 9:30 am in 146C

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