Using the Field Calculator (python) to create Full Path Name for hyperlink

Question

I'm trying to use the field calculator to populate the field "Hyperlink1" with the full path name of the document.  I have a field called "DOC_NO" and if there is a document number in it, I would like the field "Hyperlink1" to fill in the path name with the document number.  If there is no text in "DOC_NO" I do not want any text in the "Hyperlink1" field.  But I can't seem to get it work right.  Can anyone take a look?

Pre-Logic Script Code:

def myfunction(docno) :
 if len(!DOC_NO!) == 0 :
    return ''"
  else:
    return "V:\Eng\Land Management\Easements\Scanned Documents\" + !DOC_NO! + ".tif"

Hyperlink1=
myfunction( !DOC_NO! )

curtvprice · Answer

Darren is correct; you can't use the "!field!" syntax inside the function. And Bruce too...

Here's my solution. This would work with either numeric or text fields.

I like to use only one "return" (for readability).

Pre-Logic Script Code:def myfunction(docno):
  docno = str(docno).strip() # remove any trailing spaces
  if len(docno).strip() == 0:
    val = ""
  else:
    # the "r" is needed
    val = r"V:\Eng\Land Management\Easements\Scanned Documents\" + docno + ".tif"
  return val

Hyperlink1 =myfunction( !DOC_NO! )

BruceNielsen · Answer

If you are going to use backslashes in a string, you need to identify it as a raw string:
return r"V:\Eng\Land Management\Easements\Scanned Documents\" + docno + ".tif"

so Python doesn't try to interpret the next character as a control character.

DarrenWiens2 · Answer

Outside of your function, you're in ArcGIS world - so you correctly use "!DOC_NO!" to reference the field, which passes each value, then "docno", to the function one at a time. Inside the function, you're in Python world, so you use the variable "docno".def myfunction(docno) :
   if len(docno)== 0 :
     return ""
   else:
     return "V:\Eng\Land Management\Easements\Scanned Documents\" + docno + ".tif"

edit: also, check your quotes after the first return - you've got two single quotes, then a double quote.