René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"base64.b64decode error raised on valid input","articleBody":"# Bug report\n\n### Bug description:\n\nAn error is raised for the following valid test cases using the newly introduced `ignorechars` parameter\n```python\nimport base64\n\nassert base64.b64decode(b'/----', altchars=b'-+', ignorechars=b'/') == b'\\xfb\\xef\\xbe'\nassert base64.b64decode(b'+----', altchars=b'/-', ignorechars=b'+') == b'\\xff\\xff\\xff'\n```\n\nFor both we get:\n```\nbinascii.Error: Invalid base64-encoded string: number of data characters (5) cannot be 1 more than a multiple of 4\n```\nIn both cases, the leading byte should be ignored thus giving a 4 bytes valid input.\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-145969\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/mayeut","@type":"Person","name":"mayeut"},"datePublished":"2026-03-15T08:51:05.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/145968/cpython/issues/145968"}