topic Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”, in ArcGIS Pro Questions

ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JamalNUMAN — Fri, 29 Jul 2022 09:05:55 GMT

ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

I couldn’t figure out why the python expression below fails to perform on “field calculator

!A! + "/"+ !B!

This expression is supposed to combine the field A and field B in field C. The first value in the C table when computed is assumed to be 33 / 1

What could be the issue here?

The gdb file is attached

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

Luke_Pinner — Fri, 29 Jul 2022 09:23:38 GMT

The error message is telling you that you can't add a string to a number. The "+" operator is for adding numbers or concatenating strings, not adding or concatenating strings to numbers.

Use string formatting instead:

C = f"{!A!} / {!B!}" # or C = "{} / {}".format(!A!, !B!) # or C = "%s / %s" % (!A!, !B!)

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JohannesLindner — Fri, 29 Jul 2022 09:29:50 GMT

A and B are floats, "/" is a string.

In Python, addition between float and str isn't defined, so the Field Calculator doesn't know what to do.

You have to convert the floats to strings using one of these methods:

# explicitly cast the floats to strings str(!A!) + "/" + str(!B!) # implicitly cast to string with str.format() "{}/{}".format(!A!, !B!) # implicitly cast to string with format string f"{!A!}/{!B!}"

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JamalNUMAN — Fri, 29 Jul 2022 15:31:59 GMT

The expression (str(!A!) + "/" + str(!B!)) adds one decimal number for each number.

How to eliminate this decimal number?

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JoshuaBixby — Fri, 29 Jul 2022 18:57:12 GMT

You are making it harder than it has to be. Just don't wrap your Python division character in a string. For example:

!A! / !B!

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

Luke_Pinner — Fri, 29 Jul 2022 23:03:23 GMT

@JoshuaBixby then will the result be the division of the two numbers (not what OP wants) instead of a string with the two numbers separated by a forward slash (what the OP wants)?

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

Luke_Pinner — Fri, 29 Jul 2022 23:02:28 GMT

Again, use string formatting

f"{!A!:.0f} / {!B!:.0f}" "{:.0f} / {:.0f}".format(!A!, !B!) "%.0f / %.0f" % (!A!, !B!)

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JamalNUMAN — Sat, 30 Jul 2022 11:04:40 GMT

Thank you for the help. It works fine

Re: ArcGIS Pro 2.8.4: A python expression fails to perform on “field calculator”,

JoshuaBixby — Sat, 30 Jul 2022 13:17:05 GMT

@Luke_Pinner, I was too quick skimming over the question, thanks for pointing out the real question.