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I'm working on writing a script that will calculate facility ID's for feature classes in a feature dataset. Is there a way to do this without making feature layers and doing select/field calculate operations on all of them?

Basically, I'm wanting to iterate through the feature dataset and create a list of feature classes that can then have the field calc ran on each. The problem is that each feature class has a different expression for field calculation, and I need to select only null values, and the select layer by attribute function requires a feature layer.

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    It's not hard to make a feature layer from a feature class, read resources.arcgis.com/en/help/main/10.2/index.html#//… about MakeFeatureLayer. Your question is a little to vague to be helpful in any specific way; are you looking for a particular field that has Null values? Making a feature layer with a where clause '<field> is NULL' coupled with int(arcpy.GetCount_management(YourFeatureLayer).getOutput(0)) will very quickly give you an idea of how many features have a null in their <field>. – Michael Stimson Jul 3 '18 at 3:11
  • Make an attempt using da.UpdateCursor and post a new question if you get stuck and include your code attempt. – BERA Jul 3 '18 at 8:03
  • I just need to calculate facility ID's for every feature class in a feature dataset, all using a common field. The problem is that each feature class has a different method if calculating the ID's. I'll try the update cursor. Thanks, guys! – Tyler Smith Jul 3 '18 at 12:06
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I would not use the Field Calculator for this. Instead I would use an arcpy.da.UpdateCursor():

UpdateCursor establishes read-write access to records returned from a feature class or table.

Returns an iterator of lists. The order of values in the list matches the order of fields specified by the field_names argument.

You will need to write various if/elif/else statements, use ListFeatureClasses, etc to complete your code.

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