HELP! Need to generate an exclusion rule at the beginning of the python script based on values from a specific field of a gdb

Question

I am working on a file GDB containing polygons with multiple fields and values. One of the text fields of that GDB is filled by applying a python script that uses the information of many other fields to generate the text values.
That script works very well, but I need to add an exclusion rule at the beginning  so it will not be applied on certain polygons based on specific values from a certain field (the goal is not to overwrite the values of those polygons which values are gonna be manually written before running the script).
In applied words, the script gives an Ecosystem name for each polygon based on biological and geomorphological field values, but I don't want the script to be processed on polygons that contains validation data from a certain source. In that case, it means I don't want it to be processed when the ''Validation'' field equals 4 specific values (which are specific sources of validation), because those Ecosystem names have to and are written manually before running the script and I don't want to overwrite them.  (See the screenshot I've joined)

I should specify that I am not the one that wrote the script initially. The person left so I need to find my way around and I am a complete beginner in python scripting. I was hoping someone could give me a hand and tell me if there is a straightforward way for this. Thank you!!!

Begining of the script.JPG

Example.jpg

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Laurence · Answer

That would have been a good tip, but I want it to be part of the script, because other people in time will be applying it and I don't want to risk to overwrite anything. But thanks for your answer! 😉

JohannesLindner · Answer

Your screenshot shows how the variable "ecosystem" is calculated, but not how it is written into the feature class.

I understand that you don't want to post the whole script, but to help you, we need to know how the field is written.

Please tell us:

* Dou you run the script in the Python Window in ArcGIS?* If yes: ArcMap or ArcGIS Pro?
* If yes: Do you need the feature class loaded in the map as a layer?

* Do you run the script as a standalone script (e.g. double click or from the command line or a Python IDE)?

Please look for code blocks that include any of the following and post them:

* arcpy.da.UpdateCursor
* arcpy.UpdateCursor
* arcpy.CalculateField_management
* arcpy.management.CalculateField

curtvprice · Answer

One thing to keep in mind is that when you run any tool on a layer or table vies it only applies to the selected set of rows. So if the polygon code that is "filling values" is working on a layer, you can apply a selection to the layer or table view before executing your script.