'Solution'

app/cafe.py

@@ -0,0 +1,21 @@
+import datetime
+from app.errors import (
+    NotVaccinatedError,
+    OutdatedVaccineError,
+    NotWearingMaskError
+)
+
+
+class Cafe:
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+
+    def visit_cafe(self, visitor: dict) -> str:
+        if "vaccine" not in visitor:
+            raise NotVaccinatedError
+        if datetime.date.today() > visitor["vaccine"]["expiration_date"]:
+            raise OutdatedVaccineError
+        if not visitor["wearing_a_mask"]:
+            raise NotWearingMaskError
+        return f"Welcome to {self.name}"

app/errors.py

@@ -0,0 +1,17 @@
+class VaccineError(Exception):
+    pass
+
+
+class NotVaccinatedError(VaccineError):
+    def __str__(self) -> str:
+        return "Visitor is not vaccinated"
+
+
+class OutdatedVaccineError(VaccineError):
+    def __str__(self) -> str:
+        return "Vaccine is outdated"
+
+
+class NotWearingMaskError(Exception):
+    def __str__(self) -> str:
+        return "Visitor is not wearing a mask"

app/main.py

@@ -1 +1,16 @@
-# write your code here
+from app.cafe import Cafe
+from app.errors import VaccineError, NotWearingMaskError
+
+
+def go_to_cafe(friends: list[dict], cafe: Cafe) -> str:
+    not_wearing_masks = 0
+    for visitor in friends:
+        try:
+            cafe.visit_cafe(visitor)
+        except NotWearingMaskError:
+            not_wearing_masks += 1
+        except VaccineError:
+            return "All friends should be vaccinated"
+    if not not_wearing_masks:
+        return "Friends can go to KFC"
+    return f"Friends should buy {not_wearing_masks} masks"