Syntax Error Label Expression Debug

Question

I'm attempting to debug a code for a conditional label expression. The code is based on one i have previously used and did not have any issues. The python code is as follows.

def FindLabel ( [TF], [INV_1], [DIR_1], [INV_2], [DIR_2], [INV_3], [DIR_3], [INV_4], [DIR_4], [INV_5], [DIR_5], [INV_6], [DIR_6] ):
 return def FindLabel ( [TF], [INV_1], [DIR_1], [INV_2], [DIR_2], [INV_3], [DIR_3], [INV_4], [DIR_4], [INV_5], [DIR_5], [INV_6], [DIR_6]):
 myLabel = "TF {0}".format([TF])
 if not [INV_1] is None:
myLabel += "\nINV {0}".format([INV_1]) & [DIR_1]
 if not [INV_2] is None:
myLabel += "\nINV {0}".format([INV_2]) & [DIR_2]
 if not [INV_3] is None:
myLabel += "\nINV {0}".format([INV_3]) & [DIR_3]
 if not [INV_4] is None:
myLabel += "\nINV {0}".format([INV_4]) & [DIR_4]
 if not [INV_5] is None:
myLabel += "\nINV {0}".format([INV_5]) & [DIR_5]
 if not [INV_6] is None:
myLabel += "\nINV {0}".format([INV_6]) & [DIR_6]
 return myLabel

Where TF, INV_1, INV_2, INV_3, INV_4, INV_5, and INV_6 are numbers, and DIR_1, DIR_2, DIR_3, DIR_4, DIR_5, and DIR_6 are text, all have the potential to be null. When I click "OK" arcgis returns the following error

The expression contains an error. 
Modify the expression and try again. 
Error 0 on line 0. 
Syntaxerror: invalid syntax (<string>, line 2).

Coding is far from my strong suit.

Answer 1

There are a number of issues in your code. The error message is referring to the first issue it found - if you that issue you'd get an error for the next. I'll try to outline them all for you here (hopefully I don't miss any).

1. Your second line shouldn't be there. Remove this line

   return def FindLabel ( [TF], [INV_1], [DIR_1], [INV_2], [DIR_2], [INV_3], [DIR_3], [INV_4], [DIR_4], [INV_5], [DIR_5], [INV_6], [DIR_6]):
   

2. Your indentation is messed up. Python is very particular about indentation, so be sure it's correct.

   This is incorrect:

    if not [INV_1] is None:
   myLabel += "\nINV {0}".format([INV_1]) & [DIR_1]
   

   As your myLabel += ... is part of the if block, you need to indent the second line further than the first line

    if not [INV_1] is None:
    myLabel += "\nINV {0}".format([INV_1]) & [DIR_1]
   

   Additionally, the line if not [INV_6] is None: is not indented far enough - it should line up with all the other if lines.

3. I'm unsure what you're trying to do with the & in "\nINV {0}".format([INV_1]) & [DIR_1]. As far as I know, the ampersand in python is not used with text (see Stack Overflow Q&A What does & mean in python).
   It appears that you are trying to concatenate the two field values together - if so, put the [DIR_1] into your string format as well - something like this

   if not [INV_1] is None:
    myLabel += "\nINV {0}{1}".format([INV_1], [DIR_1])
   

4. While not an issue that would cause an error, this is tidier and easier to read. Instead of if not [INV_1] is None:, use if [INV_1]:. Basically you're saying "if INV_1 isn't false" which is the same as saying "if INV_1 is true"

   if [INV_1]:
    myLabel += "\nINV {0}{1}".format([INV_1], [DIR_1])
   

I think the following update to your script should work better

def FindLabel ([TF], [INV_1], [DIR_1], [INV_2], [DIR_2], [INV_3], [DIR_3], [INV_4], [DIR_4], [INV_5], [DIR_5], [INV_6], [DIR_6]):
 myLabel = "TF {0}".format([TF])
 if [INV_1]:
 myLabel += "\nINV {0}{1}".format([INV_1], [DIR_1])
 if [INV_2]:
 myLabel += "\nINV {0}{1}".format([INV_2], [DIR_2])
 if [INV_3]:
 myLabel += "\nINV {0}{1}".format([INV_3], [DIR_3])
 if [INV_4]:
 myLabel += "\nINV {0}{1}".format([INV_4], [DIR_4])
 if [INV_5]:
 myLabel += "\nINV {0}{1}".format([INV_5], [DIR_5])
 if [INV_6]:
 myLabel += "\nINV {0}{1}".format([INV_6], [DIR_6])
 return myLabel