UniqueValuesFromAttributeTable.py

in_table = 'C:\Users\mpodebradska2\Documents\ArcGIS\Thesis_New\Table.dbf'
field_names = ['Plan_Name', 'Plan_Nam_1', 'Plan_Nam_2', 'Plan_Nam_3']
all_values = []

with arcpy.da.SearchCursor(in_table,field_names) as cursor:
  for row in cursor:
    all_values.extend(list(row))
    
unique_values = set(all_values)
print unique_values

file = open("Table.txt","w")
file.write("\n ".join(unique_values))
file.close()