Adding time to variable using Python Parser of ArcGIS Calculate Value tool?

Question

I am using Python 2.7 in calculate value in ModelBuilder. I want to query both 30 seconds before and after the variable. The original value keeps returning not the time change. What am I not defining?

Expression ("%Da%")

Code Block:

def getsecond():
    from datetime import datetime
    getsecond == ("%Da%")+ timedelta(seconds=30)
    return getsecond

type string

The variable Da is a date field

Answer 1

1. Despite being a date field, the "Da" field would be treated as unicode within the Field Calculator. You may need to first convert the field value to datetime format, as described here: https://stackoverflow.com/questions/22219210/convert-the-unicode-to-datetime-format?rq=1
2. While you have defined a function, you are not calling it, and the function itself has no way of knowing what the field value is.
3. There is a chance that having the local variable getsecond be named the same as the function getsecond is causing problems.
4. Python field names should be surrounded by ! in Calculate Field.
5. You have an operand that would return True/False (==) not a new calculated value (=)

Some suggestions:

Change Expression to updateSecond(!Da!)

Change Code Block to:

from datetime import datetime
def updateSecond(datefield):
    getsecond = datefield + timedelta(seconds=30)
    # May instead have to do something like the following:
    # assumes field values looks like u'2014-03-06T04:38:51Z' in the example
    # getsecond = datetime.strptime(datefield, '%Y-%m-%dT%H:%M:%SZ')
    return getsecond

Answer 2

I implemented all of @smiller’s suggestions. I had to change the order of the lines so that it formatted before calling the function but the below now works.

from datetime import datetime, date, time, timedelta
def updateSecond(Da):
    then = datetime.strptime(Da, '%m/%d/%Y %I:%M:%S %p')
    sec = timedelta(seconds=30)
    updateSecond = then + sec
    # May instead have to do something like the following:
    # assumes field values looks like u'2014-03-06T04:38:51Z' in the example
    updateSecond =  datetime.strptime(Da, '%m/%d/%Y %I:%M:%S %p')
    updateSecond = then + sec
    return updateSecond