none-coalesce operator¶

a ?? b evaluates to a when a is not None, otherwise to b:

name = user.display_name ?? "anonymous"

transpiles to:

name = __by_t_0__ if (__by_t_0__ := user.display_name) is not None else "anonymous"

a compound left operand is bound to a temp by the walrus so it is evaluated exactly once. a bare name needs no temp and is repeated directly — a ?? b is a if a is not None else b

semantics¶

?? tests is not None (identity) — not falsiness. an empty string, zero, or an empty list is not coalesced. only None triggers the fallback

precedence¶

?? has the same precedence as a conditional expression — it binds looser than or / and / arithmetic and tighter than assignment. parenthesize when mixing with boolean operators

interaction with ?.¶

see optional chaining. ?? and ?. compose; complex left operands are evaluated at most once even when chained