ArcPy is a Python site package that provides a useful and productive way to perform geographic data analysis, data conversion, data management, and map automation with Python. ArcGIS applications and scripts written using ArcPy, benefit from being able to access and work with the numerous Python modules developed by GIS professionals and programmers from many different disciplines. The additional power of using ArcPy within Python is that Python is a general-purpose programming language that is easy to learn and use. It is interpreted and dynamically typed, which gives you the ability to quickly prototype and test scripts in an interactive environment while still being powerful enough to support the writing of large applications.
# Importing arcpy # import arcpy # Set the workspace environment and run Clip_analysis arcpy.env.workspace = 'C:/Data/Tongass' arcpy.Clip_analysis('standb4', 'clipcov', 'standby_clip', 1.25)
Once you have imported ArcPy, you can run all geoprocessing tools found in the standard toolboxes installed with ArcGIS.
A module is a Python file that generally includes functions and classes. ArcPy is supported by a series of modules, including a data access module (arcpy.da), a mapping module (arcpy.mp), an ArcGIS Spatial Analyst module (arcpy.sa), and an ArcGIS Network Analyst module (arcpy.na).
To import an entire module, use the import module:
# Import only arcpy.mp # import arcpy.mp
Of course, Python has many other core and third-party modules. If you wanted to also work with Python's core os and sys modules, you may use a similar import:
# Import arcpy, os and sys # import arcpy import os import sys
In many cases, you may not plan or need to use the entire module. One way to import only a portion of a module is to use a from-import statement. The example below imports the env class (the env class contains all the geoprocessing environments). Now, instead of having to access environments as arcpy.env, you can simplify it as env..
# Import env from arcpy and set the workspace environment # from arcpy import env env.workspace = 'c:/data'
Following the same thought process, sometimes you may want to draw attention to what a module or part of a module is identified as to make your script more readable, or perhaps the default name is too long for your preferences. In any of these cases, you can use the form from-import-as. Like the previous example, the example below also imports the env class but assigns it the name ENV:
# Import env from arcpy as ENV and set the workspace environment # from arcpy import env as ENV ENV.workspace = 'c:/data'
You can import the mapping module in the same fashion:
# Import the mapping module from arcpy as MAP and create an ArcGISProject # object # from arcpy import mp as MAP aprx = MAP.ArcGISProject('c:/Projects/YosemiteNP/Yosemite.aprx')
Another version of importing is the form from-import-*. The contents of the module import directly into the namespace, meaning you can then use all those contents directly without needing to prefix them. For example:
# Import management from arcpy as * # from arcpy.management import *
However, there are some risks associated with this approach. Other objects, variables, modules, and so forth, with the same name are overwritten, not to mention that with large modules, your namespace can become particularly crowded and busy. Think about it this way, in the following example, both the management and analysis module are imported as *. Both of these modules have a Clip tool. If you now try to use Clip, which Clip are you actually using? The answer is the second one, but this approach can lead to uncertainty and difficulty in reading the script.
# Import the management and analysis modules from arcpy as * # from arcpy.management import * from arcpy.analysis import * # Which Clip is it? # Clip('standb4', 'clipcov', 'standby_clip', 1.25)
However, in some cases, from-import-* can simplify your code, as in the case of the ArcGIS Spatial Analyst's sa module. One of the benefits of the sa module is that you can nest multiple classes and functions in a single line to produce an output raster object.
# Import arcpy and the sa module as * # import arcpy from arcpy.sa import * # Get input parameters # inRaster1 = arcpy.GetParameterAsText(0) inRaster2 = arcpy.GetParameterAsText(1) inRaster3 = arcpy.GetParameterAsText(2) outRaster = (Raster(inRaster1) + (Raster(inRaster2) - Raster(inRaster3)))
Now compare the next code block, which uses the conventional import-from statement. Now imagine adding a few more classes and functions into the code. The addition of sa for every function and class adds up quickly, disrupting the readability and adding more bulk to the line.
# Import arcpy and the sa module # import arcpy from arcpy import sa # Get input parameters # inRaster1 = arcpy.GetParameterAsText(0) inRaster2 = arcpy.GetParameterAsText(1) inRaster3 = arcpy.GetParameterAsText(2) outRaster = (sa.Raster(inRaster1) + (sa.Raster(inRaster2) - sa.Raster(inRaster3)))