paul j3 <[email protected]> added the comment:
Another way to play with the defaults is to use argparse.SUPPRESS. With such a
default, the argument does not appear in the namespace, unless provided by the
user.
In [2]: p = argparse.ArgumentParser()
...: p.add_argument('--foo', default=argparse.SUPPRESS, help='foo help')
...: p.add_argument('--bar', default='default')
...: p.add_argument('--baz');
In [3]: args = p.parse_args([])
In [4]: args
Out[4]: Namespace(bar='default', baz=None)
Such a namespace can be used to update an existing dict (such as from a config
file), changing only keys provided by user (and ones where SUPPRESS does not
make sense, such as store_true and positionals).
In [5]: adict = {'foo':'xxx', 'bar':'yyy', 'baz':'zzz'}
In [6]: adict.update(vars(args))
In [7]: adict
Out[7]: {'foo': 'xxx', 'bar': 'default', 'baz': None}
User provided value:
In [8]: args = p.parse_args(['--foo','foo','--baz','baz'])
In [9]: args
Out[9]: Namespace(bar='default', baz='baz', foo='foo')
In this code sample I used Ipython. That IDE uses (or at least did some years
ago) a custom integration of config and argparse. System default config
file(s) set a large number of parameters. Users are encouraged to write their
own profile configs (using provided templates). On starting a session, the
config is loaded, and used to populate a parser, with arguments, helps and
defaults. Thus values are set or reset upto 3 times - default, profile and
commandline.
I for example, usually start an ipython session with an alias
alias inumpy3='ipython3 --pylab qt --nosep --term-title
--InteractiveShellApp.pylab_import_all=False
--TerminalInteractiveShell.xmode=Plain'
Regarding this bug/issue, if someone can come up with a clever tweak that
satisfies Thermi, is potentially useful to others, and is clearly backward
compatible, great.
But if this issue requires a less-than-ideal-compatible patch, or greater
integration of config and argparse, then it needs to be developed as a separate
project and tested on PyPi. Also search PyPi; someone may have already done the
work.
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<https://bugs.python.org/issue44748>
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