Is somebody able to explain this strange python behavior? >>> from collections import defaultdict >>> d = defaultdict(lambda: "foo") >>> d >>> defaultdict(<function <lambda> at 0x732ae877a480>, {}) >>> d["x"] >>> 'foo' >>> d >>> defaultdict(<function <lambda> at 0x732ae877a480>, {'x': 'foo'}) I interpret d[x] as a read access. However, the value of x gets stored in the dict, which is indeed a write access. Is this some caching mechanism for long evaluating lambdas? Now, when I use .get(...) instead of indexing, behaviour is different: >>> d.get("y") >>> <None> >>> d >>> defaultdict(<function <lambda> at 0x732ae877a480>, {'x': 'foo'}) This time y is not stored in the dict and the returned value is None instead of foo. This is even more confusing as the value returned by d.get("y") or d["y"] is dependent on the order of the invocation of both. Continue reading...
