Merging feature classes in memory gives ERROR 001156?

Question

arcpy.AddField_management("in_memory/originalfc","ALPHABET","TEXT",1)
arcpy.Select_analysis("in_memory/originalfc","in_memory/A","attr<=0")
arcpy.CalculateField_management("in_memory/A","ALPHABET",'"A"',"PYTHON")
arcpy.Select_analysis("in_memory/originalfc","in_memory/B","attr>0")
arcpy.CalculateField_management("in_memory/B","ALPHABET",'"B"',"PYTHON")
arcpy.Merge_management(["in_memory/A","in_memory/B"],"in_memory/merged")

When the merge executes I get an error 001156 on OID 1 that says i can't write value 'A' to output field ALPHA.

If I try to append one to the other I get the same error. They were originally the same feature class why won't they go back together?

Answer 1

IN_MEMORY is a sort of simplified "geodatabase" but obviously in memory not on a disk. Now the important thing to appreciate is that it is like a geodatabase and thus honours the many specification, but not all, of a geodatabase.

I believe you have been unlucky enough to have chosen a geodatabase RESERVED field name, ALPHA. Suggest you call it something else like "myALPHA".

Answer 2

I got this error again and the reason it is coming up for me has to do with domains and in_memory feature classes and combining datasets in arcpy.

Example:

FeatureClass1 has attribute [NAME] with a coded value of "MR" and the domain shows "Mister" (that fc was a selection from a larger dataset and the domain assigned in the gdb carried over to the in_memory)

FeatureClass2 has attribute [NAME] with a value of "MR" no domain attached

If I merge the two I get error 001156. If I append FeatureClass1 to FeatureClass2 I get error 001156.

But if I append FeatureClass2 to FeatureClass1 it works!