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

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

JohnPapageorgiou — Thu, 13 Aug 2020 17:49:42 GMT

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

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

KoryKramer — Thu, 13 Aug 2020 18:09:30 GMT

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

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

JohnPapageorgiou — Thu, 13 Aug 2020 18:17:33 GMT

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

thanks,

John

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

JohnPapageorgiou — Thu, 13 Aug 2020 18:18:32 GMT

Looks like you moved it for me, thank you!

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

KoryKramer — Thu, 13 Aug 2020 19:47:38 GMT

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

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

DanPatterson — Thu, 13 Aug 2020 20:50:39 GMT

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

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

JohnPapageorgiou — Thu, 13 Aug 2020 22:08:30 GMT

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

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

DanPatterson — Sat, 11 Dec 2021 17:20:27 GMT

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"""‍‍‍‍

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

JohnPapageorgiou — Thu, 08 Oct 2020 07:03:44 GMT

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

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

BibhashNath — Sun, 04 Apr 2021 06:29:28 GMT

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)

-----------

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

Anonymous User — Sun, 04 Apr 2021 12:42:33 GMT

Is that - before the summed_total in your actual script (-summed_total = ... )? if it is, then the name 'summed_total' wouldn't exist.

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

BibhashNath — Sun, 04 Apr 2021 14:19:02 GMT

it was typos... not working even after removing this..

###Codes:

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

# This part is working to get my percent (I manually included sumtotal in my exp)
per_exp = "(!sum_tract!/1836082531.0221872)*100"
arcpy.AddField_management("summary_tract_2", "test1", "SHORT")
arcpy.CalculateField_management("summary_tract_2", "test1", per_exp)

# This part is NOT working to get my percent (here sumtotal selected in the func)
per_exp = "my_percent(!Sum_tract!, summed_total)"
codeblock = """
def my_percent(area, tot):
return area/tot * 100"""
# Add Field & Calculate Field
arcpy.AddField_management("summary_tract_2", "test2", "SHORT")
arcpy.CalculateField_management("summary_tract_2", "test2",
per_exp, "PYTHON3", codeblock)

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

JoshuaBixby — Sun, 04 Apr 2021 15:24:11 GMT

This part is NOT working

It is helpful to elaborate when saying something isn't working because there are lots of ways something can be broken and not work. Are you getting an error message? If so, what, and include the traceback. Are you getting unexpected results? If so, what do you expect and what are you getting?

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

BibhashNath — Sun, 04 Apr 2021 15:30:42 GMT

it says...

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

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

JoshuaBixby — Sun, 04 Apr 2021 16:11:08 GMT

I am a bit confused because all of your code uses "summed_total" but the error message references "sum_total". Do you have both "summed_total" and "sum_total" variables? If not, why is the error message referencing a different variable name than in your code snippet?

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

BibhashNath — Sun, 04 Apr 2021 16:35:16 GMT

summed_area = sum((r[0] for r in arcpy.da.SearchCursor("summary_eff_area", ['area'])))
print(summed_area)

per_exp = "my_percent(!area!, summed_area)"

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

# CalculateField
arcpy.CalculateField_management("summary_eff_area", "percent",
per_exp, "PYTHON3", codeblock)

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

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

BibhashNath — Sun, 04 Apr 2021 16:57:42 GMT

got it done!! by another approach...

To calculate percentage: area to percent

total = float(sum(row[0] for row in arcpy.da.SearchCursor("summary_eff_area", 'area')))
print(total)
with arcpy.da.UpdateCursor("summary_eff_area", ('area', 'percent')) as uCursor:
for area, percent in uCursor:
uCursor.updateRow([area, (area / total)*100])

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

JoshuaBixby — Sun, 04 Apr 2021 17:49:03 GMT

I am glad you got it working with an update cursor. I mocked up some similar code as yours and ran it in the interactive Python window with no issues using Pro 2.7, so maybe it is either something related the version you are using or how or where you are calling the code from.

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

BibhashNath — Mon, 05 Apr 2021 23:14:58 GMT

Thanks... could you please share your code to compare line by line ...
in my case even sometimes same code do stop working..

Bibhash

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

JoshuaBixby — Tue, 06 Apr 2021 17:29:47 GMT

I basically just copied your code and updated the field names. I was running it in the interactive Python window in Pro, is that where you are running the code from?

Regarding:

in my case even sometimes same code do stop working.

If your code sometimes works and sometimes doesn't, than the issue likely isn't your code and something else because valid code is valid code.