No boolean traps
Why it matters copy(src, dst, True, False) cannot be read without opening the function. Swap the two flags and a dry run becomes a real overwrite. Named options make every call say what it does.
A data team has a helper that copies records between two stores: copy_records(src, dst, overwrite, dry_run). Last month someone called it as copy_records(a, b, False, True) meaning "dry run, do not overwrite", got the order wrong, and overwrote a production table. You are replacing it.
Boolean trap: an argument that is only True or False, so the call site does not say what it means and is easy to swap.
copy_records(src, dst, on_conflict="keep", mode="dry_run")Write copy_records(src, dst, *, on_conflict, mode). src and dst are dicts. For each key in src: if it is not in dst, copy it; if it is, on_conflict decides: "keep" (leave dst's value), "overwrite" (use src's), or "fail" (raise ValueError and change nothing at all). mode is "apply" (change dst) or "dry_run" (change nothing). Return the sorted list of keys written (or that would be).
Hidden misuse scripts will try each of these; each must raise TypeError or ValueError and leave dst unchanged: passing the options by position, leaving either option out (no defaults: the caller must choose), any value that is not exactly one of the named strings (typos, other capitals, True, False, None), and the old overwrite= keyword.
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