I am trying to use Python in ArcGIS Pro to cleanse some data via imported Excel sheets. The expression works, but the Code Block if-else statement to return nothing if !Street_Id! is returns an error.


str(!Street_ID!) + ' ' + !Street!.split("/")[0] 

Code Block

def f(x): ' '
if !Street_ID! = 'Null'
return x
else return str(!Street_ID!) + ' ' + !Street!.split("/")[0]


File"<string>",line 2
if!Street_ID! = 'Null'
SynatxError: invalid syntax

Results using the expression in Python IDLE

2 Answers 2


There's a bunch of things wrong with your code:

  • Incorrect code invocation
  • Incorrect function definition (placing a non-comment to the right of the colon)
  • Poor function naming (far better to keep everything you use, so you don't have to debug every time you use it, but that requires descriptive naming)
  • Failure to pass in the values to be used in the expression string
  • No indentation (required part of the Python language)
  • Failure to place a space between the if keyword and logical expression
  • Using assignment (=) instead of equivalence (==) for a logical test
  • Using expression field delimiters in Python code
  • Assuming a NULL value will match the string 'Null' (instead it maps to None)
  • Improper use of early exit (after a return you don't need an else)
  • Performing string math (using format is best practice)

When the smoke clears, the corrected result looks like this:

Expression: usefulName(!Street!,!StreetID!,'nullValue')

Expression type: Python

Code block:

def usefulName(street_val,street_id,x):
    if (street_id == None):
        return x
    return "{:s} {:s}".format(street_id,street_val.split("/")[0])

If you want to avoid early exit (some organizations/programs forbid it as confusing), then the code block would look like:

def usefulName(street_val,street_id,x):
    result = x
    if (street_id != None):
        result = "{:s} {:s}".format(street_id,street_val.split("/")[0])
    return result

And the ternary logic form would look like:

def usefulName(street_val,street_id,x):
    return "{:s} {:s}".format(street_id,street_val.split("/")[0]) if street_id else x

Which actually compresses down to a simple Python expression of:

"{:s} {:s}".format(!StreetID!,!Street!.split("/")[0]) if !StreetID! else 'nullValue'

though that's probably a bit obscure for reuse.


You need a double equal sign, a colon at the ends, and proper indentation for sure.

Consider writing your code in a Python IDE that shows syntax errors during code development.

 def f(x):
    if !Street_ID! == 'Null':
        return x
        return str(!Street_ID!) + ' ' + !Street!.split("/")[0]
  • 2
    !Street! and !Street_ID! should be passed into function f as parameters (f(!Street!,!StreetID!,'defVal'), and function f should be defined with three parameters def f(street_val,street_id,x) and therefore won't have the bang sandwich inside the function (return str(street_id) + ' ' + street_val.split("/")[0])
    – Vince
    Commented Jun 18, 2020 at 18:43
  • Thanks for catching that.
    – GBG
    Commented Jun 18, 2020 at 18:54
  • I am going to research to comprehend the way Vince explained passing into functions as parameters and defining the f function with parameters and will post my answer after the fact, I get what he is saying generally when using parameters, but at the same time I need to comprehend how to script it out and why it needs to be expressed in the code block concerning indentation. I did catch onto the bang sandwich at least.
    – cheff_
    Commented Jun 18, 2020 at 20:17

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