Syntax when passing variable to calculate field expression

ZacharyHart

OK, so I feel like I've tried just about everything here. What I'm looking to do is to concatenate a iteration value (?) from a search cursor with the object ID of a feature class to create a unique ID field. I want these two values separated by a hyphen '-'. Target field (PLOT_ID) is obviously a string. There is what I've got working so far.

i = 1

ptCur = arcpy.da.SearchCursor (ptFC, fldLst)

for row in ptCur:

[various things happen removed for brevity]

Cluster_Plot = str(i) + '!OBJECTID!'

arcpy.AddMessage(Cluster_Plot)

arcpy.CalculateField_management(outPointsDissolve,"PLOT_ID",Cluster_Plot,"PYTHON_9.3")

things are appended to a a target FC and the target field looks like this:

So it appears to be treating the expression inputs as strings. From here I've tried to get a - in between the two values with no luck....even when converting the OID to a string : 'str(!OBJECTID!)'   I just can't get things to escape right i guess. Things I've tried:

Cluster_Plot = str(i) + '-' + '!OBJECTID!'

Here the  hyphen apparently is interpreted as an operator:

Cluster_Plot = str(i) + " + '-' + " + '!OBJECTID!'

Cluster_Plot = str(i) + " + '-' + " + 'str(!OBJECTID!)'

I dont get this because you can use the + operator in the field calculator just fine (if you format the field as a string using str)

Could someone please help me out of my misery here?

MicahBabinski

Hi Zachary,

Would

Cluster_Plot <SPAN class="operator token">=</SPAN> <SPAN class="string token">'"{}-{}"'</SPAN><SPAN class="punctuation token">.</SPAN>format<SPAN class="punctuation token">(</SPAN>i<SPAN class="punctuation token">,</SPAN><SPAN class="string token">'!OBJECTID!'</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

work? I've become a big fan of using triple quoted strings and the .format() method when creating a variable to use as a field calculator expression.

Another option is to use an update cursor. Something like:

table <SPAN class="operator token">=</SPAN> <SPAN class="string token">"myTable"</SPAN>
fields <SPAN class="operator token">=</SPAN> <SPAN class="punctuation token">(</SPAN><SPAN class="string token">"OBJECTID"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"PLOT_ID"</SPAN><SPAN class="punctuation token">)</SPAN>
i <SPAN class="operator token">=</SPAN> <SPAN class="number token">1</SPAN>
<SPAN class="keyword token">with</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>da<SPAN class="punctuation token">.</SPAN>UpdateCursor<SPAN class="punctuation token">(</SPAN>table<SPAN class="punctuation token">,</SPAN> fields<SPAN class="punctuation token">)</SPAN> <SPAN class="keyword token">as</SPAN> cursor<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">for</SPAN> row <SPAN class="keyword token">in</SPAN> cursor<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN> <SPAN class="operator token">=</SPAN> str<SPAN class="punctuation token">(</SPAN>i<SPAN class="punctuation token">)</SPAN> <SPAN class="operator token">+</SPAN> <SPAN class="string token">"-"</SPAN> <SPAN class="operator token">+</SPAN> str<SPAN class="punctuation token">(</SPAN>row<SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cursor<SPAN class="punctuation token">.</SPAN>updateRow<SPAN class="punctuation token">(</SPAN>row<SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; i<SPAN class="operator token">+=</SPAN><SPAN class="number token">1</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

Good luck!