Added example solutions to several chapters. Feel free to create a pull request with your answers. Also for the chapters that have no solutions yet :)

CH_06_decorators/exercise_05/solution_00.py

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+# Create a version of `functools.cached_property` that can be recalculated 
+# as needed.
+from datetime import datetime
+
+
+class _NotFound:
+    pass
+
+
+class CachedProperty:
+    # Note that this is a very basic version of `functools.cached_property`. If
+    # you wish to use this in production I suggest looking at the original
+    # `cached_property` decorator and implement the locking and conflict
+    # handling as well.
+
+    def __init__(self, func):
+        self.func = func
+
+    def clear(self):
+        self.cache.pop(self.attrname, None)
+
+    def __set_name__(self, owner, name):
+        if not hasattr(owner, '_cache'):
+            owner._cache = dict()
+            # Add a clear method to the owner class
+            setattr(owner, f'clear_{name}', self.clear)
+
+        self.cache = owner._cache
+        self.attrname = name
+
+    def __get__(self, instance, owner=None):
+        if instance is None:
+            return self
+
+        key = self.attrname
+        if key not in self.cache:
+            self.cache[key] = self.func(instance)
+
+        return self.cache[key]
+
+
+class SomeClass:
+
+    @CachedProperty
+    def current_time(self):
+        return datetime.now()
+
+
+def main():
+    some_class = SomeClass()
+    a = some_class.current_time
+    b = some_class.current_time
+    assert a == b
+    # Clear the cache. Even though your editor might complain, this method
+    # exists. Can you think of a better API to make the cache clearable?
+    some_class.clear_current_time()
+    c = some_class.current_time
+    assert a != c
+
+
+if __name__ == '__main__':
+    main()