actually, only

  dict(d1, **d2)

has that problem. it works fine if you unpack into a dict literal:

  >>> d1 = {1: 'a'}
  >>> d2 = {2: 'b'}
  >>> {**d1, **d2}
  {1: 'a', 2: 'b'}

iirc the pep mostly just says that it's suboptimal because it's syntactically heavy/noisy, non-obvious and can't be overloaded in dict subclasses

---

i was curious why the two double-stars behave differently despite syntactic similarity. so i went and checked the bytecode, and it turns out they compile down to different opcodes! `{××d1, ××d2}` yields a BUILD_MAP_UNPACK, while `dict(d1, ××d2)` yields a CALL_FUNCTION_EX/CALL_FUNCTION_KW (depending on the CPython version)