Add lazy dict class draft

yt_dlp/utils/lazy_infodict.py

@@ -0,0 +1,76 @@
+from collections.abc import MutableMapping
+
+from yt_dlp.utils import try_call
+
+
+class LazyInfoDict(MutableMapping):
+    def __init__(self, data=None, lazy=None):
+        self._data = data or {}
+        self._lazy = lazy or {}
+
+        for key in self._data.keys() & self._lazy.keys():
+            del self._lazy[key]
+
+        self._data.update(dict.fromkeys(self._lazy.keys()))
+
+    def __contains__(self, key):
+        return key in self._data
+
+    def __getitem__(self, key):
+        if key in self._lazy:
+            compute_func = self._lazy[key]
+
+            print(f"Evaluating key {key!r}")
+            updates = try_call(compute_func, expected_type=dict) or {}
+            self._data.update(updates)
+            for update in updates:
+                self._lazy.pop(update, None)
+
+        return self._data[key]
+
+    def __setitem__(self, key, value):
+        if key in self._lazy:
+            del self._lazy[key]
+
+        self._data[key] = value
+
+    def __delitem__(self, key):
+        if key in self._lazy:
+            del self._lazy[key]
+
+        del self._data[key]
+
+    def __iter__(self):
+        return iter(self._data)
+
+    def __len__(self):
+        return len(self._data)
+
+    def __repr__(self):
+        data = f"{self._data!r}"
+        if self._lazy:
+            data += f", lazy={set(self._lazy.keys())!r}"
+        return f"{type(self).__name__}({data})"
+
+
+if __name__ == '__main__':
+    def eval_test():
+        print('eval_test')
+        return {'test': 'test'}
+
+    def eval_else():
+        print('eval_else')
+        return {'something': 'something', 'else': 'else'}
+
+    data = LazyInfoDict({
+        'nonlazy': 'nonlazy',
+        'attribute': 'attribute',
+    }, {
+        'test': eval_test,
+        'something': eval_else,
+        'else': eval_else,
+    })
+    print(f'{data["else"]=}')
+    print('-----')
+    for key, value in data.items():
+        print(f'data[{key!r}]={value!r}')