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Render underscores as hyphens in CLI option names #921

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Merged
jph00 merged 1 commit into from
Aug 26, 2026
Merged

Render underscores as hyphens in CLI option names #921

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5 changes: 3 additions & 2 deletions fastcore/script.py
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ def main(msg:Annotated[str, "The message"],

## Short flags

A capital letter in a parameter name declares a short flag: the capitalized letter becomes the short spelling and the lowercased name the long one, so `Resume:int=None` gets both `-r` and `--resume`. The capital can be any letter (`sUggest:str=None` gives `-u/--suggest`), only the first capital counts, and names without capitals get a long flag only. Since the flags are lowercased, the parameter's actual name keeps its capital -- so a Python caller writes `main(Resume=3)`, which usefully advertises that it's invoking a CLI entry point. Positional (default-less) parameters have no flags, so capitals there are left alone.
A capital letter in a parameter name declares a short flag: the capitalized letter becomes the short spelling and the lowercased name the long one, so `Resume:int=None` gets both `-r` and `--resume`. The capital can be any letter (`sUggest:str=None` gives `-u/--suggest`), only the first capital counts, and names without capitals get a long flag only. Underscores in optional parameter names appear as hyphens (`cache_dir` becomes `--cache-dir`), while the Python argument keeps its underscore. Since the flags are lowercased, the parameter's actual name keeps its capital -- so a Python caller writes `main(Resume=3)`, which usefully advertises that it's invoking a CLI entry point. Positional (default-less) parameters have no flags, so capitals there are left alone.

## Positional params

Expand Down Expand Up @@ -141,7 +141,7 @@ def _arg_kw(k, anno, doc, default, extra, mv=None):
else: action,d = 'store_true',False
if action=='version':
if 'version' not in extra and d is not inspect.Parameter.empty: extra['version'] = d
return f'--{k}', {'help':doc or '', **extra}
return f'--{k.replace("_", "-")}', {'help':doc or '', **extra}
kw = {}
if action and 'action' not in extra: kw['action'] = action
if anno is not None:
Expand All @@ -154,6 +154,7 @@ def _arg_kw(k, anno, doc, default, extra, mv=None):
kw['help'] = (doc or '') + (f" (default: {dshow})" if 'default' in kw else '')
if negated: kw['dest'] = k
name = f'no-{k}' if negated else k
if opt: name = name.replace('_', '-')
short = first(c for c in k if c.isupper()) if opt else None
if short is None: return f"{'--' if opt else ''}{name}", {**kw, **extra}
kw['dest'] = k # flags are lowercased, so argparse's derived dest would drop the capital
Expand Down
9 changes: 5 additions & 4 deletions nbs/06_script.ipynb
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Expand Up @@ -140,7 +140,7 @@
"#| export\n",
"## Short flags\n",
"\n",
"A capital letter in a parameter name declares a short flag: the capitalized letter becomes the short spelling and the lowercased name the long one, so `Resume:int=None` gets both `-r` and `--resume`. The capital can be any letter (`sUggest:str=None` gives `-u/--suggest`), only the first capital counts, and names without capitals get a long flag only. Since the flags are lowercased, the parameter's actual name keeps its capital -- so a Python caller writes `main(Resume=3)`, which usefully advertises that it's invoking a CLI entry point. Positional (default-less) parameters have no flags, so capitals there are left alone."
"A capital letter in a parameter name declares a short flag: the capitalized letter becomes the short spelling and the lowercased name the long one, so `Resume:int=None` gets both `-r` and `--resume`. The capital can be any letter (`sUggest:str=None` gives `-u/--suggest`), only the first capital counts, and names without capitals get a long flag only. Underscores in optional parameter names appear as hyphens (`cache_dir` becomes `--cache-dir`), while the Python argument keeps its underscore. Since the flags are lowercased, the parameter's actual name keeps its capital -- so a Python caller writes `main(Resume=3)`, which usefully advertises that it's invoking a CLI entry point. Positional (default-less) parameters have no flags, so capitals there are left alone."
]
},
{
Expand Down Expand Up @@ -295,7 +295,7 @@
" else: action,d = 'store_true',False\n",
" if action=='version':\n",
" if 'version' not in extra and d is not inspect.Parameter.empty: extra['version'] = d\n",
" return f'--{k}', {'help':doc or '', **extra}\n",
" return f'--{k.replace(\"_\", \"-\")}', {'help':doc or '', **extra}\n",
" kw = {}\n",
" if action and 'action' not in extra: kw['action'] = action\n",
" if anno is not None:\n",
Expand All @@ -308,6 +308,7 @@
" kw['help'] = (doc or '') + (f\" (default: {dshow})\" if 'default' in kw else '')\n",
" if negated: kw['dest'] = k\n",
" name = f'no-{k}' if negated else k\n",
" if opt: name = name.replace('_', '-')\n",
" short = first(c for c in k if c.isupper()) if opt else None\n",
" if short is None: return f\"{'--' if opt else ''}{name}\", {**kw, **extra}\n",
" kw['dest'] = k # flags are lowercased, so argparse's derived dest would drop the capital\n",
Expand Down Expand Up @@ -371,9 +372,9 @@
"metadata": {},
"outputs": [],
"source": [
"test_eq(_arg_kw('a', int, 'help', 1, {}), ('--a', dict(type=int, default=1, help='help (default: 1)')))\n",
"test_eq(_arg_kw('some_flag', int, 'help', 1, {}), ('--some-flag', dict(type=int, default=1, help='help (default: 1)')))\n",
"test_eq(_arg_kw('a', int, 'help', inspect.Parameter.empty, {}), ('a', dict(type=int, help='help')))\n",
"test_eq(_arg_kw('up', bool, 'upper?', True, {}), ('--no-up', dict(action='store_false', default=True, help='upper? (default: True)', dest='up')))\n",
"test_eq(_arg_kw('some_flag', bool, 'enabled?', True, {}), ('--no-some-flag', dict(action='store_false', default=True, help='enabled? (default: True)', dest='some_flag')))\n",
"test_eq(_arg_kw('p', str, 'path', inspect.Parameter.empty, dict(opt=False, nargs='?', default='-')),\n",
" ('p', dict(type=str, default='-', help='path (default: -)', nargs='?')))\n",
"test_eq(_arg_kw('a', int, 'help', 1, {}, 'int'), ('--a', dict(type=int, default=1, help='help (default: 1)', metavar='(int)')))\n",
Expand Down