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21.01. Programming/Python/decorator.md

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+## 在decorator內取得function的default argument與class member
+```python
+import sys
+import inspect
+from functools import wraps
+
+
+def exampleDecorator(func):
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        print(f"Decorator: call by {func.__name__}")
+        def get_default_args(func):
+            signature = inspect.signature(func)
+            return {
+                k: v.default for k, v in signature.parameters.items() if v.default is not inspect.Parameter.empty
+            }
+
+        ## Get default
+        defaultKwargs = get_default_args(func)
+        defaultKwargs.update(kwargs)
+        print(f"Decorator: args = {args}, kwargs = {kwargs}, defaultKwargs = {defaultKwargs}")
+
+        objectInstance = args[0]
+        if hasattr(objectInstance, 'defaultArg1'):
+            print(f'objectInstance has defaultArg1, a.defaultArg1({type(objectInstance.defaultArg1)}) = {objectInstance.defaultArg1}')
+            if objectInstance.defaultArg1:
+                ## Do something here
+                print("Decorator: some message...")
+        else:
+            print('objectInstance does not have defaultArg1')
+
+        return func(*args, **kwargs)
+    return wrapper
+
+
+class ExampleClass():
+    def __init__(self, defaultArg1=True, defaultArg2="SomeString"):
+        self.defaultArg1 = defaultArg1
+        self.defaultArg2 = defaultArg2
+        print(f'self.defaultArg1 = {self.defaultArg1}, self.defaultArg2 = {self.defaultArg2}')
+
+    @exampleDecorator
+    def run(self, arg1=1, arg2=2):
+        print(f"ExampleClass.run(), arg1 = {arg1}, arg2 = {arg2}")
+
+example = ExampleClass()
+example.run()
+```