topic Retrieving first value in list in Python Questions

Retrieving first value in list

MikeEdwards — Fri, 20 Oct 2017 14:37:52 GMT

I'm trying to extract the first value from a list. I'm using [0] but it seems to be returning all the values regardless. Am I overlooking something?

env.workspace = r"someSDEconnection.sde"

addModDate_featureList = arcpy.ListFeatureClasses("GEO*")
for addModDate_feature in addModDate_featureList:
   fc_result = arcpy.GetCount_management(addModDate_feature)
   fc_count = int(fc_result.getOutput(0))
   if fc_count == 0:
      print(addModDate_feature + " No Geometry Present")
   else:
      addModDate_field_names = [f.name for f in arcpy.ListFields(addModDate_feature)]
      if "MOD_DATE" in addModDate_field_names:
      unique_addDate = set(row[0] for row in arcpy.da.SearchCursor(addModDate_feature, "MOD_DATE"))
      outList = []
      for element in unique_addDate:
         if element is None:
            pass
         elif element is not None and element not in outList:
            outList.append(element)
            outList.sort(reverse=True)
            outList_recent = outList[0]
            print(addModDate_feature + " " + outList_recent)

else:
print(addModDate_feature + " No Date")

Re: Retrieving first value in list

MitchHolley1 — Sat, 11 Dec 2021 09:34:27 GMT

1.) Add brackets around your search cursor fields

2.) Remove the 'elif element is not None' from the elif statement since you're already checking if it's None in the above 'if' statement.

3.) Use the GeoNet Syntax Highlighter.

nv.workspace = r"someSDEconnection.sde"
addModDate_featureList = arcpy.ListFeatureClasses("GEO*")
for addModDate_feature in addModDate_featureList:
   fc_result = arcpy.GetCount_management(addModDate_feature)
   fc_count = int(fc_result.getOutput(0))
   if fc_count == 0:
      print(addModDate_feature + " No Geometry Present")
   else:
      addModDate_field_names = [f.name for f in arcpy.ListFields(addModDate_feature)]
      if "MOD_DATE" in addModDate_field_names:
      #add [] around the fields you're searching
      unique_addDate = set(row[0] for row in arcpy.da.SearchCursor(addModDate_feature, ["MOD_DATE"]))
      outList = []
      for element in unique_addDate:
        if element is None:
            pass
        elif element not in outList: #leave out checking if None, since that happens in 'if' above
            outList.append(element)
            outList.sort(reverse=True)
            outList_recent = outList[0]
            print(addModDate_feature + " " + outList_recent)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Retrieving first value in list

JoshuaBixby — Fri, 20 Oct 2017 15:19:26 GMT

I assume the bolded part is where you are having the issue. At first glance, I am not sure why using the zero index is retrieving more than one value. I ran a mock up using most of your code and didn't have an issue. If you can put some print statements in and provide the community more feedback about values of variables along the way, we might be able to help more.

Re: Retrieving first value in list

JoshuaBixby — Fri, 20 Oct 2017 15:22:30 GMT

If one is only passing a single field to a cursor, it doesn't have to be a list. That said, passing a list regardless of the number of fields is a more consistent approach than a string for a single field and list for multiple fields.

Re: Retrieving first value in list

MikeEdwards — Sat, 11 Dec 2021 09:34:29 GMT

env.workspace = r"someSDEconnection.sde"

addModDate_featureList = arcpy.ListFeatureClasses("GEODBA*")
for addModDate_feature in addModDate_featureList:
    fc_result = arcpy.GetCount_management(addModDate_feature)
    fc_count = int(fc_result.getOutput(0))
    if fc_count == 0:
        print(addModDate_feature + " No Geometry Present")
    else:
        addModDate_field_names = [f.name for f in arcpy.ListFields(addModDate_feature)]
        if "MOD_DATE" in addModDate_field_names:
            unique_addDate = set(row[0] for row in arcpy.da.SearchCursor(addModDate_feature, ["MOD_DATE"]))
            outList = []
            for element in unique_addDate:
                if element is None:
                    pass
                elif element not in outList:
                   outList.append(element)
                   outList.sort(reverse=True)
                else:
                    pass
            if len(outList) == 0:
                pass
            else:
                outList_recent = outList[0]
                print(addModDate_feature + " " + str(outList_recent))‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

If I test for the Lists with no values it seems to work fine.

Re: Retrieving first value in list

RhettZufelt — Sat, 11 Dec 2021 09:34:32 GMT

This one I still use the old cursors as it is so simple.

myField = "recnum"
maxValue = arcpy.SearchCursor(infc, "", "", "", "recnum D").next().getValue(myField) #Get 1st row in descending cursor sort
‍‍‍‍‍‍‍‍

Only loading one field into the searchcursor, and in this case, it is numeric, so if I grab the first value, is the max, change the sort to "A" and would be the min. In any case, it grabs the first value in the list.