How to Set up an expression in arcpy to calculate percent where one of the variables is the result of a previous calculation

[JohnPapageorgiou]

Hi,

I have a feature class with two fields I am interested in using.  One field is "area_acres" and the other is "Survey_Pcnt".  I have calculated the field "area_acres".  My intent is to sum all the values in the field "area_acres" and then use that "summed_total" in the following expression to calculate the "Survey_Pcnt" field:  "!area_acres!/summed_total*100".  I have managed to sum all the values successfully, but when I try to add summed_total as a variable in the expression and run the script I get the error: TypeError: unsupported operand type(s) for /: 'str' and 'float'.  This error leads me to believe I'm trying to perform division between a string and floating point which wouldn't work.  Below is my code that I'm having trouble with.

summed_total = sum((r[0] for r in arcpy.da.SearchCursor(env.workspace + "/APE_intersect_dissolve_adequacy", ['area_acres'])))
print (summed_total)

percentage_expression = "(float(!area_acres!))"/float(summed_total)*"(float(100))"

arcpy.CalculateField_management(env.workspace + "/APE_intersect_dissolve_adequacy","Survey_Pcnt", percentage_expression, "PYTHON_9.3")

I have tried writing the percentage_expression many different ways to no avail.  At this point any help is greatly appreciated. Let me know if there is any other information I can provide.  I am using ArcGIS desktop 10.7.1 and arcpy.

thank you,

John

[KoryKramer]

Hi John.  This would be a good question for the Python‌ space!

[JohnPapageorgiou]

Thank you Kory.  Can you tell me how to get it there?

thanks,

John

[JohnPapageorgiou]

Looks like you moved it for me, thank you!

[KoryKramer]

No worries.  Yeah, I figured the @mention would make it show up in that space so hopefully somebody there can help!

[DanPatterson]

e = float(!area_acres!)/float(summed_total) * float(100)

Will return a correct numeric value, now if the expression needs to be quoted, add the quotes to this.  You had too many

[JohnPapageorgiou]

Hi Dan,

thank you for your reply unfortunately e = float(!area_acres!)/float(summed_total) * float(100) gives me a syntax error which I'm trying to resolve.  When I put double quotations around the whole expression, the variables become strings and the float command does not work.  I'll keep trying and responses are still welcome.

thank you,

John

[DanPatterson · Accepted solution]

maybe you have to emulate a codeblock and expression

Calculate Field (Data Management)—ArcGIS Pro | Documentation 

exp = "do_stuff(!area_acres!, summed_total)"
codeblock = """
def do_stuff(area, tot):
    return area/tot * 100"""‍‍‍‍

[JohnPapageorgiou]

Hi Dan,

That worked with the condition of adding a new field of the total area and calculating it first.  So all fields need to be created and populated before I can use the above code block.  I was interested in a method of using the sum of the areas without having to create a new field and populate it with area sums (that are the same value).  Otherwise it worked.

thank you,

John

[BibhashNath]

I have a similar question and I tried to do the same as yours but my code is not working...

ExecuteError: ERROR 000539: Traceback (most recent call last):
  File "<expression>", line 1, in <module>
NameError: name 'summed_total' is not defined

Failed to execute (CalculateField).

-summed_total = sum((r[0] for r in arcpy.da.SearchCursor("summary_tract_2", ['Sum_tract'])))
print(summed_total)

per_exp = "my_percent(!Sum_tract!, summed_total)"

codeblock = """
def my_percent(area, tot):
return area/tot * 100"""

print(codeblock)
# Execute AddField
arcpy.AddField_management("summary_tract_2", "test", "SHORT")

# Execute CalculateField
arcpy.CalculateField_management("summary_tract_2", "test",
per_exp, "PYTHON3", codeblock)

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