Which answer is correct?

Use `a.update(b)` — it adds all keys from b into a.

— py_veteran

Use `a | b` (Python 3.9+). It returns a new merged dict without modifying either original.

— modern_python

Use `dict(a, **b)`. This creates a new dict with both sets of keys.

— clever_py

Use `{**a, **b}`. Works in Python 3.5+ and returns a new dict.

— unpacking_fan