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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`,` works with `Decimal()` against the doc of **Format Specification Mini-Language**","articleBody":"# Bug report\n\n### Bug description:\n\n[The doc](https://docs.python.org/3/library/string.html#format-specification-mini-language) of **Format Specification Mini-Language** doesn't say that `,` works with [Decimal()](https://docs.python.org/3/library/decimal.html#decimal.Decimal) as shown below:\n\n\u003e ',': Inserts a comma every 3 digits for integer presentation type 'd' and floating-point presentation types, excluding 'n'. For other presentation types, this option is not supported.\n\nBut `,` works with `Decimal()` against the doc as shown below:\n\n```python\nfrom decimal import Decimal\n\nv = Decimal(value='1234.5555555555')\n\nprint('\"{:,.20f}\"'.format(v))\nprint('\"{:,.20F}\"'.format(v))\n# \"1,234.55555555550000000000\"\n#        |        20        |\n\nprint('\"{:,f}\"'.format(v))\nprint('\"{:,F}\"'.format(v))\n# \"1,234.5555555555\"\n#        |   10   |\n```\n\n```python\nfrom decimal import Decimal\n\nv = Decimal('123456.78912')\n\nprint('\"{:,.20g}\"'.format(v))\nprint('\"{:,.20G}\"'.format(v))\nprint('\"{:,.20}\"'.format(v))\nprint('\"{:,g}\"'.format(v))\nprint('\"{:,G}\"'.format(v))\nprint('\"{:,}\"'.format(v))\n# \"123,456.78912\"\n#  |    11     |\n```\n\nIn addition, the doc doesn't say that `_` works with `Decimal()` as shown below:\n\n\u003e '_': Inserts an underscore every 3 digits for integer presentation type 'd' and floating-point presentation types, excluding 'n'. For integer presentation types 'b', 'o', 'x', and 'X', underscores are inserted every 4 digits. For other presentation types, this option is not supported.\n\nSo, `_` doesn't work with `Decimal()` as the doc doesn't say so as shown below:\n\n```python\nfrom decimal import Decimal\n\nv = Decimal(value='1234.5555555555')\n\nprint('\"{:_.20f}\"'.format(v))\nprint('\"{:_.20F}\"'.format(v))\nprint('\"{:_f}\"'.format(v))\nprint('\"{:_F}\"'.format(v))\n# ValueError: invalid format string\n```\n\n```python\nfrom decimal import Decimal\n\nv = Decimal('123456.78912')\n\nprint('\"{:_.20g}\"'.format(v))\nprint('\"{:_.20G}\"'.format(v))\nprint('\"{:_.20}\"'.format(v))\nprint('\"{:_g}\"'.format(v))\nprint('\"{:_G}\"'.format(v))\nprint('\"{:_}\"'.format(v))\n# ValueError: invalid format string\n```\n\n### CPython versions tested on:\n\n3.12\n\n### Operating systems tested on:\n\nWindows","author":{"url":"https://github.com/hyperkai","@type":"Person","name":"hyperkai"},"datePublished":"2025-07-13T22:10:07.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/136636/cpython/issues/136636"}