caculate field python invaild syntax

[WilliamYu811]

Hi there,

I'm a newbie for python, trying to fill the <Null>  into 04 by using the "Caculate Field" function.

But it says I got some invaild syntax, not sure what's goion on after searching some tutorials on the internet.

I wan't to know how to make it work, thanks.

Sincerely,

Teng-Wei.

[DanPatterson · Accepted solution]

re  .... is the name of a python module change the function name, or perhaps use the following

  

[BarryNorthey]

Dan's method above of selecting target records and then calculating on the selected records is a safe, easy and effective way to do this. Be sure to work on a copy of data when experimenting or alternately make sure that Undo is enabled so you can Discard edits when things go wrong.

Consider the option below:

Python is fussy about indentation and colons:

[DanPatterson]

!LOC! if !LOC! else "04"

Will do the same since <NULL> is effectively None

emulating a file in a table called LOC

LOC =['A', 'B', None, "D"]

[i if i else "04" for i in LOC]
Out[12]: ['A', 'B', '04', 'D']

[JoshuaBixby]

As pointed out by @BarryNorthey the specific syntax error you are getting is due to a lack of a colon after your function definition line.

Since you are new to Python, I will also point out that best practice according to https://peps.python.org/pep-0008/ :

Comparisons to singletons like None should always be done with is or is not, never the equality operators.

So, in this case your syntax should not be

if ( LC01 == None ) :   # which by the way you forgot another colon.

but should be

if ( LC01 is None ) :

As @DanPatterson has already pointed out, for a simple conditional check like this you can rely on Python's conditional expression, aka ternary operator, to handle it rather than defining a function in the code block. 

"04" if !LC01! is None else !LC01!