The PEP [1] addresses this: Few people would be able to guess what it means the first time they see it, or think of it as the "obvious way" to merge two dicts

The PEP [1] addresses this: Few people would be able to guess what it means the first time they see it, or think of it as the "obvious way" to merge two dicts [...] {d1, d2} ignores the types of the mappings and always returns a dict. type(d1)({d1, d2}) fails for dict subclasses such as defaultdict that have an incompatible __init__ method. Though I'm not personally convinced that + would be more obvious or that dict subtypes are merged often enough for this to matter. [1] https://www.python.org/dev/peps/pep-0584/#d1-d2 https://www.python.org/dev/peps/pep-0584/#d1-d2