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Improve default value handling in help messages #235

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17 changes: 14 additions & 3 deletions src/argh/constants.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
"""

import argparse
import io

__all__ = (
"ATTR_NAME",
Expand Down Expand Up @@ -78,6 +79,10 @@ def _expand_help(self, action):
Ideally this could be achieved by simply defining
:attr:`DEFAULT_ARGUMENT_TEMPLATE` as ``{default!r}`` but unfortunately
argparse only supports the old printf syntax.

If the default value is None or False, don't show it.
If the default value stdin or stdout, show the name not the repr.
If the default value is another file handle, show <class name>.
"""
params = dict(vars(action), prog=self._prog)
for name in list(params):
Expand All @@ -95,14 +100,20 @@ def _expand_help(self, action):
# an IndexError in _format_action)
#
if "default" in params:
if params["default"] is None:
params["default"] = "-"
if params["default"] in [None, False]:
action.default = argparse.SUPPRESS
elif isinstance(params["default"], io.IOBase):
if hasattr(params["default"], "name"):
params["default"] = params["default"].name
else:
params["default"] = f"<{params['default'].__class__.__name__}>"
else:
params["default"] = repr(params["default"])
#
# /

return self._get_help_string(action) % params
string = self._get_help_string(action) % params
return string


#: Default formatter (:class:`CustomFormatter`) to be used in implicitly
Expand Down