Python If Statements

[nbreese9]

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?

 

[JayantaPoddar]

Codeblock:

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

Expression:

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

[Brian_Wilson]

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. 

[Anonymous User]

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!)