Using an IF statement in Field Calculator

Question

I'm trying to use an if statement in the field calculator: This is what the code looks like in Python:

a= 2 
FacilityID= !FACILITYID! 
if a%2==0:
 MH_ID_Calc=FacilityID[0:6]
else:
 MH_ID_Calc=FacilityID[7:14]
print MH_ID_Calc

06M244

so I tried to run that in ArcGIS field calculator:

def myCalc(FID,FACID):
if FID%2==0:
return FACID[0:6]
else:
return FACID[7:14]
myCalc( !FID! !FACILITYID!)

But it fails each time.

• Midavalo: Welcome to GIS SE! As a new user please take the tour to learn about our focused Question and Answer format. Please check your indentation - there are no indents in your field calculator code above, but python needs the indents. Also double-check that you've selected the Python Parser in field calculator.
• Midavalo: What happens when you run the field calculator? There should be result messages under Geoprocessing > Results
• mkennedy: Check out this question and answer which probably makes this a duplicate.
• Bjorn: myCalc(!FID!, !FACILITYID!)? There's a comma missing when you call the function
• Aaron: Please edit your question to include the error message.

Answer 1

As others have already commented, the parameters of the function call in your expression should be comma separated:

myCalc(!FID!, !FACILITYID!)

And you must use correct indentation with Python (unlike other languages, this is part of Python syntax, and it will not work if the indentation is not correct):

def myCalc(FID,FACID):
 if FID%2==0:
 return FACID[0:6]
 else:
 return FACID[7:14]

Ie, anywhere that a line ends with a colon (:) represents a new code block and the next line should be indented further. All lines within a block must have exactly the same indentation, unless they are part of a sub-block, in which case, they must have the exact same indentation as the other lines a the same level of that sub-block.