1. class InMemoryDatabase:
2.     def _init_(self):
3.         self.database = {}
4.  
5.     def set(self, timestamp, key, field, value):
6.         if key not in self.database:
7.             self.database[key] = {}
8.         self.database[key][field] = value
9.  
10.     def compare_and_set(self, timestamp, key, field, expected_value, new_value):
11.         if key in self.database and field in self.database[key]:
12.             current_value = self.database[key][field]
13.             if current_value == expected_value:
14.                 self.database[key][field] = new_value
15.                 return "true"
16.         return "false"
17.  
18.     def compare_and_delete(self, timestamp, key, field, expected_value):
19.         if key in self.database and field in self.database[key]:
20.             current_value = self.database[key][field]
21.             if current_value == expected_value:
22.                 del self.database[key][field]
23.                 return "true"
24.         return "false"
25.  
26.     def get(self, timestamp, key, field):
27.         if key in self.database and field in self.database[key]:
28.             return self.database[key][field]
29.         return None
30.  
31.     def scan(self, timestamp, key):
32.         if key in self.database:
33.             fields = sorted(self.database[key].keys())
34.             return ", ".join([f"{field}({self.database[key][field]})" for field in fields])
35.         return ""
36.  
37.     def scan_by_prefix(self, timestamp, key, prefix):
38.         if key in self.database:
39.             fields = sorted(filter(lambda f: f.startswith(prefix), self.database[key].keys()))
40.             return ", ".join([f"{field}({self.database[key][field]})" for field in fields])
41.         return ""
42.  
43. # Example usage:
44. db = InMemoryDatabase()
45. queries = [
46.     ["SET", "0", "A", "BC", "4"],
47.     ["SET", "10", "A", "BD", "5"],
48.     ["SET", "20", "A", "C", "6"],
49.     ["SCAN_BY_PREFIX", "30", "A", "B"],
50.     ["SCAN", "40", "A"],
51.     ["SCAN_BY_PREFIX", "50", "B", "B"]
52. ]
53.  
54. for query in queries:
55.     operation = query[0]
56.     if operation == "SET":
57.         db.set(*query[1:])
58.     elif operation == "COMPARE_AND_SET":
59.         print(db.compare_and_set(*query[1:]))
60.     elif operation == "COMPARE_AND_DELETE":
61.         print(db.compare_and_delete(*query[1:]))
62.     elif operation == "GET":
63.         print(db.get(*query[1:]))
64.     elif operation == "SCAN":
65.         print(db.scan(*query[1:]))
66.     elif operation == "SCAN_BY_PREFIX":
67.         print(db.scan_by_prefix(*query[1:]))