Merging Strings for a new key

[DEWright_CA]

So I am updating a working in 10.8.1; before we migrate to Pro. I have a couple existing values (quarter and year_2dig) that we use. I an wanting to do something like this:

valuePrefix = "Q" + str(quarter) + str(year_2dig) + "_"

Then 

arcpy.CalculateField_management(loccode_fc, "QRTR_KEY", '"valuePrefix !OBJECTID!"', "PYTHON","")

So I would have a new unique value that says Q122_1 ... etc for each row

But instead I get "colPrefix + 1" as the value...  Ideas?

[DuncanHornby]

It looks like you are erroneously embedding your string within the string and using the wrong python parser,

Your code should be:

valuePrefix = "Q" + str(quarter) + str(year_2dig) + "_"
arcpy.CalculateField_management(loccode_fc, "QRTR_KEY", '"' + valuePrefix + "!OBJECTID!" + '"',"PYTHON_9.3","")

[JohannesLindner · Accepted solution]

valuePrefix = "Q" + str(1) + str(22) + "_"
'"' + valuePrefix + "!OBJECTID!" + '"'
# '"Q122_!OBJECTID!"'

That doesn't seem right.

'"' + valuePrefix + '"' + " + str(!OBJECTID!)"
# '"Q122_" + str(!OBJECTID!)'

[DEWright_CA]

Perfect; so I was close; I thought it was just a mixture of the right set of quotes and double-quotes just was running out of places to try.

[JohannesLindner]

# CalculateField can be a little hard to understand, because you have to pass
# a string that evaluates to a correct Python expression. Biggest pitfall that
# I see on this forum is concatenating strings, because people get mixed up
# with the quotation marks of their expression and the quotation marks _around_
# the expression (that make it into a string).

# It's not clear from your question where quarter and year_2dig come from,
# chose the correct expression from below. Alo, note the double quotes inside
# the expression and the single quotes to turn the expression into a string.

# if quarter and year_2dig are fields in the table, this will result in
# '"Q{}{}_{}".format(!QUARTER!, !YEAR_2DIG!, !OBJECTID!)'
expression = '"Q{}{}_{}".format(!QUARTER!, !YEAR_2DIG!, !OBJECTID!)'

# if quarter and year_2dig are python variables, this will result in
# '"Q122_{}".format(!OBJECTID!)'
expression = '"Q{}{}_'.format(quarter, year_2dig) + '{}".format(!OBJECTID!)'

arcpy.CalculateField_management(loccode_fc, "QRTR_KEY", expression, "PYTHON_9.3", "")