Have you decided to get started? It’s time to put all the assets on your side . It’s already enough complicated to learn a new language, it is useless to add pitfalls! This is a checklist and a few tips to start smoothly. Firstly , if you are accustomed to program and Python or another language leaves you completely indifferent , just take a look at the few traps described below and tackle down the Python tutorial of your choice .
On the other side, if you back off, start by convincing yourself that it is not necessary to master Python in order to use it for our tasks with ArcGis. It is quite possible to link the processing in a Python script by only knowing the basics of the language .
Get rid of the syntax Firstly, we will rely on the predictive code features by using the Python console or an integrated development environment . This allows you to have the exact syntax without having to know them by heart .
If you have not, yet, read our article ArcGis and Python before making your first steps please read it to understand the difference between python consoles that allows you to write and execute a single command line at a time, and the scripts publishers.
In ArcGis you have installed by default, the Python Console. On the other side, you have no integrated development environment by default . Therefore, you will have to install one . On the ArcGis installation support you have PythonWin . You can install it from ArrGis support. If you do not have the support at hand, you can install it from this address .
Using an IDE provides you with:
- An editor with code completion
- The syntax highlighting
- Codes of models
- A code explorer for functions and classes
- Testing tools and debugging scripts
Here we will install another IDE, PyScripter . You can download it at this address .
Why this one? Because you have to choose one and when using them, they are all quite
similar . By cons it is easier find the first big problem. Do you do not rush when
downloading the pages ! Read the following lines …
32 or64 bit ???
If you have a 32-bit machine, no problem. You can only use 32-bit
software versions .
By cons, if you have a 64-bit machine, depending on the installations chosen you
can you find, for a same software, versions 32 or 64. For example Python! And
when you go to the download page for PyScripter or PythonWin , the first thing
you have to do is to choose between the 32 or 64 bits. As it is ArcGis that installs
Python, in general you do not know which version you have . Yes, because for
ArcGIS Desktop the normally installed version, even on a 64-bit machine, is the
Python 32-bit version! By cons, if you install the 64-bit, ArcGis will install
the Python 64-bit version …
So which version do I have?
Open ArcMap, click the Python Console button, and enter both lines following : importsys
print (sys.version)
Then, you will see not only if it is 32 or 64 bits, but also the version number (2.7.x). You will need , if you install PyScrypter , at launching time because if you start with the default option, it will use the latest available version of Python (3.4). On the other side for ArcGis you must, absolutely, use version 2.7
For the curious who want to know why , here is a link Python page .
Now you have all the necessary information to download your IDE and to be able to run it for ArcGis.
How to proceed with your IDE? When you open PyScripter you have the following interface:
The goal is to describe a script that will be executed in ArcGis. The script, the succession of code lines of linking the different operations and processes , will be written in the main window.
The bottom window corresponds to the Python console. It allows you to enter a code line and run it immediately . This allows you to test the code before adding it in the main window.
Once completed and validated , you will include the script in the ArcGis Toolbox or you will create an ArcGis add-in. Theoretically, PyScripter will only be used during the development phase of the script.
Save time: Get the code samples Once you have found which tool you want to use, go to ArcGIS support and type the name of the tool . In a previous article, we have used, as example, the FeatureToLine tool . Here is what is find at the bottom of the tool support page (and this is true for all tools):
You have always a line example command with all the options and that a little script or one can see how to include this tool in a real script. Do not hesitate to “inspire” by copying and pasting the examples.
A few specifics of Python for ArcGis
Here are a few items you will not find in books or classic Python tutorials .
1- In order for your script to use ArcGis tools , start all your scripts with the line
arcpy import
2- ArcGis tools respect a Rule name strict
arcpy . the name of the tool _ the name of the toolbox that contains it
For example arcpy.FeatureToLine _management
3-In the tool syntax display, its settings are displayed in brackets . If the parameter is mandatory he will be surrounded by <> , if he is optional by {} . If the tool has multiple settings optional and you want , for example , to inform the fourth parameter optional , you are obliged to inform the three previous ones , even with chains empty .
4-Be careful with the file paths. If you use \ in the paths , that will be a problem because Python uses this symbol in her syntax . You can opt by / instead of \ ( “C: / ArcGIS / Data”) or you can double \\ in the paths ( “C; \\ ArcGis \\ Data” ). You can also to precede the chain containing a file path with r ( r “C ; \ ArcGis \ Data” ).
