[issue45673] argparse error with option with optional value

[paul j3]

paul j3  added the comment:

Put the required positional first

$ myapp myfile -s

or one of the store_true arguments

$ myapp -s -j myfile

I think

$ myapp -s -- myfile

will work as well, but that needs to be tested.  

The '-s' has to be followed by something won't be confused for an argument, 
such as nothing, or a flag.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue45673] argparse error with option with optional value

[Paolo Benvenuto]

Paolo Benvenuto  added the comment:

> As a general rule, don't use `nargs` like this where there's ambiguity as to 
> how many values will be allocated to the argument.

What could I use instead of nargs?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue45673] argparse error with option with optional value

[paul j3]

paul j3  added the comment:

https://bugs.python.org/issue9338
argparse optionals with nargs='?', '*' or '+' can't be followed by positionals

As you can see this is an old issue, but still too big for a quick fix.

As a general rule, don't use `nargs` like this where there's ambiguity as to 
how many values will be allocated to the argument.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue45673] argparse error with option with optional value

[paul j3]

paul j3  added the comment:

This is too big of an example for this board; I think it should have been asked 
on StackOverFlow.  Or maybe trimmed do to a more compact example.

But in any case, this is normal behavior for argparse.  Type checking, here 
'int', is done after the string is allocated to the '-s' argument.

Reserving that string for the required positional requires a form of look ahead 
that argparse does not currently do.  I think there's an old bug/issue on the 
topic, but the fix was, if I remember correctly, too complex to simply drop in.

I may look that up later.

--
nosy: +paul.j3

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue45673] argparse error with option with optional value

[Paolo Benvenuto]

New submission from Paolo Benvenuto :

I'm using argparse with this code:

parser = argparse.ArgumentParser(
description='Scan a media tree in order to generate cache files suitable 
for showing a beautiful web gallery',
  )
  parser.add_argument(
"config_file_or_album_path",
help="the config file, if it's the only positional argument, or the album 
path, if two positional arguments are supplied"
  )
  parser.add_argument(
"cache_path",
nargs="?",
default="",
help="the cache path, if two positional arguments are supplied; otherwise, 
nothing"
  )
  parser.add_argument(
"-s",
"--periodic-save",
nargs="?",
type=int,
const=5,
default=0,
dest="periodic_save",
metavar="MINUTES",
help="runs the scanner in a more robust way, saving json files every X 
minutes, where X is the value given, or 5 if no value is given; 0 means non 
autosaving"
  )
  parser.add_argument(
"-j",
"--recreate-json-files",
action='store_true',
dest="recreate_json_files",
help="completely recreate the json files cache"
  )
  parser.add_argument(
"-r",
"--recreate-reduced-photos",
action='store_true',
dest="recreate_reduced_photos",
help="completely recreate reduced photo cache files"
  )
  parser.add_argument(
"-t",
"--recreate-thumbnails",
action='store_true',
dest="recreate_thumbnails",
help="completely recreate thumbnail cache files"
  )
  parser.add_argument(
"-v",
"--recreate-transcoded-videos",
action='store_true',
dest="recreate_transcoded_videos",
help="completely recreate transcoded video cache files"
  )
  parser.add_argument(
"-a",
"--recreate-all",
action='store_true',
dest="recreate_all",
help="completely recreate the cache: json files, reduced photos, thumbnails 
and transcoded videos; same as -jrtv"
  )
  parser.add_argument("--version", action="version", version='%(prog)s v5.3.10')
  args = parser.parse_args()

Running the app without parameter gives me:

$ myapp
usage: scanner [-h] [-s [MINUTES]] [-j] [-r] [-t] [-v] [-a] [--version] 
config_file_or_album_path [cache_path]
myapp: error: the following arguments are required: config_file_or_album_path

(the last line doesn't matter here, a required parameter is missing).

The -s option is optional and has an optional value, but:

$ myapp -s myfile
usage: scanner [-h] [-s [MINUTES]] [-j] [-r] [-t] [-v] [-a] [--version] 
config_file_or_album_path [cache_path]
scanner: error: argument -s/--periodic-save: invalid int value: '/my/file'

I'm expecting that, since there is a mandatory positional argument, myfile is 
interpreted as such, and only after that, -s is recognized as the optional 
argument without value.

--
components: Library (Lib)
messages: 405322
nosy: paolobenve
priority: normal
severity: normal
status: open
title: argparse error with option with optional value
type: behavior
versions: Python 3.8

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com