Python Script is repeating results

Question

I have developed a python script to copy and paste in the field calculator. Having an input of three values, it compares all of them and returns a list of unique values. The problem is that when I use it in ArcMap, it only returns the first result for all the rows, even they should be different. Then, how can I evaluate each row?

Here is the code:

index =  0 
list_yes = [] 
def myFunc(var_1,var_2,var_3):

        global list_yes
        global index


    myList_1 = [var_1,var_2,var_3]
    for i in myList_1:
        myList_2 = myList_1[index:]
        for j in myList_2:
            if i == j:
                if not j:
                    pass
                else:
                    list_yes.append(j)
            elif not j:
                pass
            else:
                pass

        index = index +1

    list_set = set(list_yes)
    unique_list = list(list_set)
    return str(unique_list)

Answer 1

It is unclear if you are trying to populate a new field with the unique values from three others or if you only want to list all unique values from three columns.

To print all unique values in three fields use the set data type and da.SearchCursor (also see How to make a flat list out of list of lists?):

fc = "somefeatureclass" #Change
fields = ["field1","field2","field3"] #Change
print set([item for sublist in arcpy.da.SearchCursor(fc,fields) for item in sublist])

To calculate a new field with the unique values from three other fields on the same row use the da.UpdateCursor:

fc = "somefeatureclass"
fields = ["field1","field2","field3", "field_to_update"]

with arcpy.da.UpdateCursor(fc, fields) as cursor:
    for row in cursor:
        row[-1] = ','.join([str(a) for a in set(row[:-1])]) #Create a comma separated string with unique values
        cursor.updateRow(row)