diff --git a/lab40.py b/lab40.py
new file mode 100644
index 0000000..3eb791f
--- /dev/null
+++ b/lab40.py
@@ -0,0 +1,36 @@
+class WeekDayError(Exception):
+    pass
+
+
+class Weeker:
+    __GIORNI = ['lun', 'mar', 'mer', 'gio', 'ven', 'sab', 'dom']
+
+    def __init__(self, day):
+        if day not in Weeker.__GIORNI:
+            raise WeekDayError("Giorno non valido: " + day)
+        self.__day_index = Weeker.__GIORNI.index(day)
+
+    def __str__(self):
+        return Weeker.__GIORNI[self.__day_index].capitalize()
+
+    def add_days(self, n):
+        self.__day_index = (self.__day_index + n) % 7
+
+    def subtract_days(self, n):
+        self.__day_index = (self.__day_index - n) % 7
+
+
+# --- TEST ---
+try:
+    weekday = Weeker('lun')
+    print(weekday)
+
+    weekday.add_days(15)
+    print(weekday)
+
+    weekday.subtract_days(23)
+    print(weekday)
+
+    weekday = Weeker('lunedì')
+except WeekDayError:
+    print("Mi dispiace, non posso soddisfare la sua richiesta.")