topic Re: Passing Value for Dictionary Look Up Fails in Python Questions

Passing Value for Dictionary Look Up Fails

AmySorensen — Fri, 10 Dec 2021 22:39:06 GMT

I've a field calculator that I am trying to use that uses a csv file to look up appropriate value based on key that is passed provided to the function. As provided below, the only values calculated are zero. The code itself is loading the data and working correctly. If I enter any number into final line of code instead of "elev" it calculates the appropriate value. If I just return "elev" to see if value is getting there, it calculates the correct values. When I try the code as below, I can't get it to return the right values. Any suggestions would be appreciated.

Using ArcGIS 10.2 at ArcInfo level

What I have is below:

  import csv 
     def IDSeg(elev): 
      with open('path', mode='r') as infile:
      reader = csv.reader(infile) 
      for rows in reader: 
       k = rows[0] 
       v = rows[1] 
       lookUp = {rows[0]:rows[1] for rows in reader} 
       return lookUp.get(elev,0)

Re: Passing Value for Dictionary Look Up Fails

DanPatterson_Retired — Mon, 22 Dec 2014 03:44:12 GMT

Can you format you code using Python syntax (turn on the Advanced editor, select >>, then syntax highlighting, then Python...I know it buried in the depths of hell but that is where it is)

It is hard to see if your indentation is correct, but one glaring error is that the import statement and the def should have the same indentation

import csv

def (blah):

Re: Passing Value for Dictionary Look Up Fails

TomGeo — Mon, 22 Dec 2014 09:08:11 GMT

Hi Amy,

did you check on the type of the 'elev' that gets returned by your function?

csv.reader will give you the values as strings. Hence, there is the possibility that you are passing the correct value to dict.get() but its type is string. If I understand your explanation correct what you want is a type 'int'.

type(rows[0])

will give you the type of your key. the type of 'elev' and that of rows[0] have to be the same.

Cheers Thomas

btw.: that's pure Python and independent from any ArcGIS version. 😉

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Fri, 10 Dec 2021 22:39:09 GMT

It appears that 'elev' is passed as a float and rows[0] is a string.

I've edited the code and tested values and but I'm still not getting the correct value pulled when I try to pass the new, string value x into the function.

import csv
def IDSeg(elev):
 with open('C:\\SD.csv', mode='r') as infile:
     x = str(elev)
     reader = csv.reader(infile)
     for rows in reader:
          k = rows[0]
          v = rows[1]
          lookUp = {rows[0]:rows[1] for rows in reader}
          return lookUp.get(elev,0)

On line 10, if I substitute any of the key values my file contains directly as below it does grab the correct value.

          return lookUp.get('9970', 0)

Re: Passing Value for Dictionary Look Up Fails

DanPatterson_Retired — Mon, 22 Dec 2014 17:40:37 GMT

and you tried...

return lookUp.get(str(elev),0)

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Mon, 22 Dec 2014 17:49:09 GMT

Yes, it returns all zeros.

Re: Passing Value for Dictionary Look Up Fails

TomGeo — Mon, 22 Dec 2014 19:52:12 GMT

Can you provide us with the csv file? At this point I could only throw around wild guesses and would give it a shot myself.

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Mon, 22 Dec 2014 20:10:14 GMT

Sure thing... if only you will tell me how to attach it here...(first time posting on here if you couldn't tell.)

Re: Passing Value for Dictionary Look Up Fails

TomGeo — Mon, 22 Dec 2014 20:50:47 GMT

Go to the advanced editor... lower right corner provides a possibility to attach a file. If you can't add the csv file, then zip it and upload the zip.

Looking forward.

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Mon, 22 Dec 2014 21:08:18 GMT

I think it is a bug.

I just tried it at 10.1 on my local desktop and it ran perfectly.

Re: Passing Value for Dictionary Look Up Fails

TomGeo — Mon, 22 Dec 2014 21:17:19 GMT

Does it even work without the type casting from float to string?

Don't know... Never had a problem with the csv module or any fundamental function in Python 2.6 or later. Neither in an installation of ArcGIS nor a standalone Python installation.

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Mon, 22 Dec 2014 21:23:42 GMT

It does not work with the type casting, so that was needed.

Running the same bit of code in both locations though and it returns all '0' in 10.2 on citrix and correct values on 10.1 on local.

Thanks for all your help!

Re: Passing Value for Dictionary Look Up Fails

AmySorensen — Mon, 22 Dec 2014 21:28:29 GMT

I'm going to mark this as the correct answer, even though there is still the odd behaviour that I can not get it to run in 10.2 and I can at 10.1. I'm not sure what could be the cause of this but the typecasting was also needed.

Re: Passing Value for Dictionary Look Up Fails

TomGeo — Mon, 22 Dec 2014 21:28:46 GMT

Could you mark my suggestion for type casting then as the solution to your question. Your first question, my first answer. 😉