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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Change some implementation details in struct.Struct","articleBody":"`struct.Struct()` accepts format as a string or a bytes object. It stores the format as the bytes object, but the `format` getter returns a string (see bpo-21071/gh-65270). While not yet initialized, it stores None, since gh-78724 the getter raises RuntimeError in such case (it returned None prior to gh-65270 and crashed prior to gh-78724). The getter could also raise an UnicodeDecodeError prior to gh-145743.\n\nThis all is a Python 2 legacy. We can simply store format as a string, this will simplify the getter. We can also use NULL instead of None as the default value, and use read-only members instead of a getter. This will make the code more strightforward.\n\nThis will have user visible effects:\n\n* Non-ASCII string format will lead to ValueError (or better use struct.error?) instead of UnicodeEncodeError.\n* Non-ASCII bytes format will lead to ~UnicodeDecodeError~ ValueError instead of struct.error.\n* Getting the `format` attribute of uninitialized `Struct` will lead to AttributeError instead of RuntimeError.\n\nThese cases normally do not occur in the user code, and the current exceptions is simply an implementation detail.\n\n\u003c!-- gh-linked-prs -->\n### Linked PRs\n* gh-145851\n\u003c!-- /gh-linked-prs -->\n","author":{"url":"https://github.com/serhiy-storchaka","@type":"Person","name":"serhiy-storchaka"},"datePublished":"2026-03-12T10:05:17Z","url":"https://github.com/python/cpython/issues/145850"}