Count rows of each feature class listed in table with ArcPy?

Question

I have a table in a geodatabase: tableA

A column in that table lists a couple of feature classes that are in the geodatabase.

I want to make a loop on each name, count the number of rows in the attribute table of each feature class and store this value in a column of 'tableA'.

Here is what I've tried:

arcpy.env.workspace =r'C:\Users\user\Desktop\geodatabase\geoA.gdb'
dataset = arcpy.ListTables("tableA") #the table needed is 'tableA'
arcpy.AddField_management("tableA", "rows_count", "LONG") #create field with the count_rows
for i in dataset:
    with arcpy.da.UpdateCursor("tableA",["file_name","rows_count"]) as cur: #the fields that needed
        for row in cur:
            try:
                nrow = arcpy.GetCount_management (row[0]) #count each layer's rows
                row[1].setValue('rows_count', nrow) #fill the column with the values found
                cur.updateRow(row) #apply changes        
            except arcpy.ExecuteError as e:                     
                print(e)

AttributeError: 'NoneType' object has no attribute 'setValue'

In the result, the rows_count is null for all rows at the creation of the field.

What can be done here?

How the table looks:

file_name  rows_count
file1       null
file2       null
file3 ...   null

Question:

In the main table, how to count the number of rows for each of these files and add store this vlue in a column ?

UPDATE

Wanted output

tableA

file_name  rows_count
file1         0
file2         12
file3         1
...

Where file1,file2, etc are actual feture classes in the gdb and rows_count are the number of rows in each file.

Answer 1

Your error comes from the fact that arcpy.da returns a cursor with no method setValue. It returns a list at each iteration, that you can manipulate like a list. 'row' will contain the values of the fields selected in the cursor inside a list. Just use indice to read and write those field values (row[index] = new_value_for_the_field_at_the_specified_index).

the use of GetCount() should also be modified, because GetCount doesn't return a number but it returns an object that contains a string (don't ask me why).

and the loop on dataset is useless because you have a single table to fill.

arcpy.env.workspace =r'C:\Users\user\Desktop\geodatabase\geoA.gdb'
arcpy.AddField_management("tableA", "rows_count", "LONG") #create field with the count_rows
with arcpy.da.UpdateCursor("tableA",["file_name","rows_count"]) as cur: #the fields that needed
    for row in cur: #for each row
        try:
            #GetCount will return a "result object", the count itself is the first element of the result of getCount() 
            row[1] = int(arcpy.GetCount_management(row[0])[0]) #reads the name of feature class (check that paths are correct)
            cur.updateRow(row) #apply changes        
        except arcpy.ExecuteError as e:                     
            print(e)