default argument re-evaluation¶

a long-standing python footgun is that mutable default values ([], {}, set(), etc.) are evaluated once at function-definition time and shared across calls. basedpython removes the footgun: every non-scalar default is re-evaluated per call, so each call gets a fresh value:

def append_one(items=[]):
    items.append(1)
    return items

append_one() returns [1] every time, never the accumulating list.

scalar literals — numbers, bools, None, strings, ... — stay as plain python defaults (they're immutable, cheap, and carry no hidden state). everything else is rewritten so the default expression runs at call time.

a useful side effect: def g(a, b=a + 1) becomes valid late-bound default syntax, with b computed fresh from the actual a at each call