🔧 Adding

Visitor Design Pattern

Author: raj713335

06 Behavioral Design Patterns/10 Visitor Design Pattern.py

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+from abc import ABC, abstractmethod
+
+
+# ------------- ELEMENT INTERFACE -------------
+class GeoNode(ABC):
+    @abstractmethod
+    def accept(self, visitor: 'GeoVisitor') -> None:
+        ...
+
+
+# ------------- CONCRETE ELEMENTS -------------
+class City(GeoNode):
+    def __init__(self, name: str, population: int):
+        self.name = name
+        self.population = population
+
+    def accept(self, visitor: 'GeoVisitor') -> None:
+        visitor.visit_city(self)
+
+
+class Industry(GeoNode):
+    def __init__(self, sector: str, annual_output: float):
+        self.sector = sector
+        self.annual_output = annual_output
+
+    def accept(self, visitor: 'GeoVisitor') -> None:
+        visitor.visit_industry(self)
+
+
+class SightSeeing(GeoNode):
+    def __init__(self, name: str, rating: float):
+        self.name = name
+        self.rating = rating
+
+    def accept(self, visitor: 'GeoVisitor') -> None:
+        visitor.visit_sightseeing(self)
+
+
+# ------------- VISITOR INTERFACE -------------
+class GeoVisitor(ABC):
+    @abstractmethod
+    def visit_city(self, city: City) -> None:
+        ...
+
+    @abstractmethod
+    def visit_industry(self, industry: Industry) -> None:
+        ...
+
+    @abstractmethod
+    def visit_sightseeing(self, sight: SightSeeing) -> None:
+        ...
+
+
+# ------------- CONCRETE VISITOR: XML Export -------------
+class XMLExportVisitor(GeoVisitor):
+    def visit_city(self, city: City) -> None:
+        print(f"<city><name>{city.name}</name><population>{city.population}</population></city>")
+
+    def visit_industry(self, industry: Industry) -> None:
+        print(f"<industry><sector>{industry.sector}</sector><output>{industry.annual_output}</output></industry>")
+
+    def visit_sightseeing(self, sight: SightSeeing) -> None:
+        print(f"<sight><name>{sight.name}</name><rating>{sight.rating}</rating></sight>")
+
+
+# ------------- CONCRETE VISITOR: Stats Collector -------------
+class StatsCollectorVisitor(GeoVisitor):
+    def __init__(self):
+        self.total_population = 0
+        self.total_output = 0
+        self.total_sights = 0
+
+    def visit_city(self, city: City) -> None:
+        self.total_population += city.population
+
+    def visit_industry(self, industry: Industry) -> None:
+        self.total_output += industry.annual_output
+
+    def visit_sightseeing(self, sight: SightSeeing) -> None:
+        self.total_sights += 1
+
+    def report(self):
+        print("---- Statistics Report ----")
+        print(f"Total Population: {self.total_population}")
+        print(f"Total Industry Output: {self.total_output}")
+        print(f"Total Sightseeing Locations: {self.total_sights}")
+
+
+# ------------- CLIENT CODE -------------
+def main():
+    graph = [
+        City("New York", 8000000),
+        Industry("Tech", 500_000_000),
+        SightSeeing("Statue of Liberty", 4.9),
+        City("San Francisco", 870000),
+        Industry("Biotech", 300_000_000),
+    ]
+
+    print("=== Exporting to XML ===")
+    xml_exporter = XMLExportVisitor()
+    for node in graph:
+        node.accept(xml_exporter)
+
+    print("\n=== Collecting Stats ===")
+    stats_collector = StatsCollectorVisitor()
+    for node in graph:
+        node.accept(stats_collector)
+    stats_collector.report()
+
+
+if __name__ == "__main__":
+    main()