topic Re: Python If Statements in Python Questions

Python If Statements

nbreese9 — Fri, 10 Jun 2022 15:46:26 GMT

I am trying to do a simple if statement in ArcMap to calculate a new field. It takes the year that an attribute was rated from the "[RatingYear]" field and depending on that value, chooses the corresponding "[PASER<year>]" field value.

I want to learn more about Python coding, but can't get this to translate to Python. Is it possible to set a variable to a field value in Python?

Re: Python If Statements

JayantaPoddar — Fri, 10 Jun 2022 16:13:27 GMT

Codeblock:

def reclass(RY,P20,P21): if (RY == 2020): return P20 elif (RY == 2021): return P21 else: return 0

Expression:

reclass(!RATINGYEAR!,!PASER2020!,!PASER2021!)

Re: Python If Statements

Brian_Wilson — Fri, 10 Jun 2022 16:25:00 GMT

The syntax for fields is different, it uses ! instead of []. I find that it's better to call a function and pass the values into it so that I don't have to deal with the weird syntax in my own code, here is a snapshot for an example.

I called the variables var1 and var2 in the function and call the function in the expression below.

Translating your code would look something like this

def f(y, p2020, p2021): if y == 2020: return p2020 elif y == 2021: return p2021 return 0 PASER_CLR = f(!RATINGYEAR!, !PASER2020!, !PASER2021!)

It keeps what I am doing separate from the dataset then too in my mind it's less confusing.

Re: Python If Statements

Anonymous User — Fri, 10 Jun 2022 16:56:39 GMT

if/elif/else are good constructs and I'll just add if you have a lot of values the if/elifs can get long and get hard to follow. To get around this, you can use a dictionary lookup.

def f(y, p2020, p2021): fieldDict = {2020: p2020, 2021: p2021} # gets the key (y) or returns 0 if there is no paring. return fieldDict.get(y, 0) PASER_CLR = f(!RATINGYEAR!, !PASER2020!, !PASER2021!)