ArcPy Calculate Field – Fix ‘Cannot Convert String to Int’ Error

arcpyfield-calculator

When I load a csv file to join with ArcPy, it converts all string fields that are numeric to integers. Therefore, I have to add another field within the feature class that I'm using for joining that is an integer version of the one I originally intended to use.

There are two approaches I've tried to convert the contents of the original field to an int:

Approach 1:

arcpy.AddField_management(layerName, "BG10_INT", "LONG", 12, "", "", "", "NULLABLE", "")
expression = "toInt(!BG10!)"
codeblock = """def toInt(value):
    if value.isdigit():
        return int(value)
    else:
        return 0"""
arcpy.CalculateField_management (layerName, "BG10_INT", expression, "PYTHON", codeblock)

Approach 2:

for row in rows:
    if row.BG10.isdigit():
        row.BG10_INT = int(row.BG10)
    else:
        row.BG10_INT = 0
    rows.updateRow(row)

With either approach, I get The value type is incompatible with the field type. [BG10_INT]. How could something so simple as converting string to int be such a challenge?

After several comments and an answer suggesting I define the schema.ini file for the csv file instead of the above conversions, I tried the following approach:

Approach 3

env.workspace = "C:/data/PCA"
f = open("C:/data/PCA/schema.ini", "wb")
text = ["[bg_to_tr.csv]", "ColNameHeader=True", "Format=CSVDelimited", "Col1=BG10 Text Width 12", "Col2=PrefBUC1 Text Width 10"]
for row in text:
    f.writerow(row)

f.close()

env.qualifiedFieldNames = False
inFeatures = "C:/geodatabases/Intermediate.gdb/BG_sample"
layerName = "BG_sample_lyr"
joinTable = "bg_to_tr.csv"
joinField = "BG10"
arcpy.MakeFeatureLayer_management (inFeatures,  layerName)
outFeature = "C:/geodatabases/Intermediate.gdb/BG_sample_w_tr"
arcpy.AddJoin_management(layerName, joinField, joinTable, joinField)
arcpy.CopyFeatures_management(layerName, outFeature)

This approach only works when I join manually (sans ArcPy) within ArcMap. However, for my purpose, this needs to be done with ArcPy. Is there an explanation why this only seems to work with ArcMap? The csv file was joined without adding it directly into the ArcMap TOC.

Here is a sample of the contents of the csv file:

"BG10","PrefBUC1"
"170312106022","0002804408"
"170312106023","0002804408"
"170312105012","0002804408"

If I open the csv file in ArcMap, it recognizes schema.ini and indicates the BG10 column as a String of length 12. When I look at the join output in BG_sample_w_tr, however, it indicates that it read it as data type Double.

If it matters, neither table contains null values for the joined fields.

Best Answer

You can take care of this before ever trying to load the data into ArcGIS by creating a schema.ini file. Simply use a text editor to save a file called schema.ini (no other extension) in the same folder as your CSV. Then, explicitly specify the data types for columns that you don't want ArcGIS to infer.

For example, if your CSV were called mydata.csv and the 4th column were the one ArcGIS is loading as text, your schema.ini would look like this:

[mydata.csv]
ColNameHeader=True
Format=CSVDelimited
Col4=BG10 Long

ArcGIS always checks schema.ini files, and will therefore always correctly load the column as an integer if that is how you've specified it. If multiple CSV files are present in the same folder, they can all be controlled from the same schema.ini.

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