[issue9938] Documentation for argparse interactive use

[hai shi]

Change by hai shi :


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pull_requests: +15073
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/15362

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[issue9938] Documentation for argparse interactive use

[Milan Oberkirch]

Milan Oberkirch  added the comment:

This issue is a duplicate of issue 9112 which was resolved by commit 9375492b

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[issue9938] Documentation for argparse interactive use

[Sourav Singh]

Sourav Singh added the comment:

I would like to send a patch for the issue. How do I start

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[issue9938] Documentation for argparse interactive use

[Wolfgang Maier]

Changes by Wolfgang Maier :


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[issue9938] Documentation for argparse interactive use

[Ethan Furman]

Changes by Ethan Furman et...@stoneleaf.us:


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[issue9938] Documentation for argparse interactive use

[paul j3]

paul j3 added the comment:

The exit and error methods are mentioned in the 3.4 documentation, but there 
are no examples of modifying them.

16.4.5.9. Exiting methods
ArgumentParser.exit(status=0, message=None)
ArgumentParser.error(message)

test_argparse.py has a subclass that redefines these methods, though I think it 
is more complex than necessary.

class ErrorRaisingArgumentParser(argparse.ArgumentParser):

In http://bugs.python.org/file30204/test_intermixed.py , part of 
http://bugs.python.org/issue14191 , which creates a parser mode that is closer 
to optparse in style, I simply use:

def error(self, message):
usage = self.format_usage()
raise Exception('%s%s'%(usage, message))
ArgumentParser.error = error

to catch errors.

https://github.com/nodeca/argparse a Javascript port of argparse, adds a 
'debug' option to the ArgumentParser, that effectively redefines this error 
method.  They use that extensively in testing.

Another approach is to trap the sysexit.  Ipython does that when argparse is 
run interactively.

Even the simple try block works, though the SystemExit 2 has no information 
about the error.

try:
args = parser.parse_args('X'.split())
except SystemExit as e:
print(e)

Finally, plac ( https://pypi.python.org/pypi/plac ) is a pypi package that is 
built on argparse.  It has a well developed interactive mode, and integrates 
threads and multiprocessing.

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[issue9938] Documentation for argparse interactive use

[Ethan Furman]

Ethan Furman added the comment:

It doesn't look like xuanji has signed a CLA.

Should we create a new issue, and have someone else create a new patch, and let 
this issue just be about the docs?

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[issue9938] Documentation for argparse interactive use

[R. David Murray]

R. David Murray added the comment:

Yes, I think opening a new issue at this point might be a good idea.  The 
reason is that there are a changes either in place or pending in other issues 
that involve the parse_know_args code, so a new patch is probably required 
regardless.

I wish I had time to review and commit all the argparse patches, but so far I 
haven't gotten to them.  They are on my todo list somewhere, though :)

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[issue9938] Documentation for argparse interactive use

[Andrew Berg]

Andrew Berg added the comment:

What is the status of this? If the patch looks good, then will it be pushed 
into 3.4?

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[issue9938] Documentation for argparse interactive use

[R. David Murray]

R. David Murray added the comment:

It's great that this patch was provided.  Xuanji, can you submit a contributor 
agreement, please?

The patch is missing an update to the documentation.

(Really the patch should have been in a separate issue, as requested, since 
this one is about improving the documentation for the existing released 
versions.  I guess we'll have to open a new issue for updating the docs in the 
existing versions).

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stage:  - needs patch
versions: +Python 3.4 -Python 3.2

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[issue9938] Documentation for argparse interactive use

[Andrew Berg]

Andrew Berg added the comment:

The patch doesn't work for 3.3 (I think it's just because the line numbers are 
different), but looking over what the patch does, it looks like 
parse_known_args will return a value for args if there is an unrecognized 
argument, which will cause parse_args to call error() (it should raise 
ArgumentError instead).

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[issue9938] Documentation for argparse interactive use

[Steven Bethard]

Steven Bethard steven.beth...@gmail.com added the comment:

Looks good to me.

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[issue9938] Documentation for argparse interactive use

[Xuanji Li]

Xuanji Li xua...@gmail.com added the comment:

Updated previous patch with test cases and renamed exit_on_argument_error flag 
to exit_on_error.

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Added file: http://bugs.python.org/file22172/issue9938_with_test.patch

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[issue9938] Documentation for argparse interactive use

[Ezio Melotti]

Ezio Melotti ezio.melo...@gmail.com added the comment:

FWIW unittest had a similar issue and it's been solved adding an 'exit' 
argument to unittest.main() [0].

I think using an attribute here might be fine.
The patch contains some trailing whitespace that should be removed, also it 
might be enough to name the attribute exit_on_error.
It should also include tests to check that the attribute is set with the 
correct default value and that it doesn't raise SystemExit when the attribute 
is False.

[0]: http://docs.python.org/library/unittest.html#unittest.main

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[issue9938] Documentation for argparse interactive use

[Xuanji Li]

Xuanji Li xua...@gmail.com added the comment:

I don't think it's best to create a new subclass to throw an ArgumentParserExit 
exception; if I read the stack trace I'd see that an ArgumentError was thrown, 
then caught, then an ArgumentParserExit was thrown, which IMHO is confusing. In 
the current design, parse_known_errors catches an ArgumentError and then exits. 
I propose that the user be optionally allowed to turn off the handling of 
ArgumentError and to handle it himself instead through an 
exit_on_argument_error flag. 

Attached patch does this. Also I think this issue falls under component 'Lib' 
too.

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components: +Library (Lib)
keywords: +patch
Added file: http://bugs.python.org/file21793/issue9938.patch

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[issue9938] Documentation for argparse interactive use

[Xuanji Li]

Changes by Xuanji Li xua...@gmail.com:


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[issue9938] Documentation for argparse interactive use

[Steven Bethard]

Steven Bethard steven.beth...@gmail.com added the comment:

In the short term, just catch the SystemExit.

In the slightly longer term, we could certainly provide a subclass, say, 
ErrorRaisingArgumentParser, that overrides .exit and .error to do nothing but 
raise an exception with the message they would have printed. We'd probably have 
to introduce a new Exception subclass though, maybe ArgumentParserExit or 
something like that.

Anyway if you're interested in this, please file a new ticket (preferably  with 
a patch). Regardless of whether we ever provide the subclass, we certainly need 
to patch the documentation to tell people how to override error and exit.

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[issue9938] Documentation for argparse interactive use

[Tan Zong Xuan]

Tan Zong Xuan tzxru...@gmail.com added the comment:

I am also trying to use argparse interactively, but in this case by combining 
it with the cmd module. So I'm doing something like below:

class MyCmd(cmd.Cmd):

parser = argparse.ArgumentParser(prog='addobject')
parser.add_argument('attribute1')
parser.add_argument('attribute2')
parser.add_argument('attribute3')

def do_addobject(self, line):
args = MyCmd.parser.parse_args(line.split())
newobject = object(args.attribute1, args.attribute2, args.attribute3)
myobjects.append(newobject)

I'm faced with the same problem that when given invalid input, parse_args exits 
the program completely, instead of exiting just to the Cmd shell. 

I have the feeling that this use case is sufficiently common such that it would 
be good if people did not have to override the exit method themselves, and 
instead an alternative to parse_args was provided that only raises exceptions 
for the surrounding code to handle rather than exiting the program entirely.

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[issue9938] Documentation for argparse interactive use

[Éric Araujo]

Éric Araujo mer...@netwok.org added the comment:

You can always catch SystemExit.

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[issue9938] Documentation for argparse interactive use

[Éric Araujo]

Éric Araujo mer...@netwok.org added the comment:

Do you want to work on a patch?

(Aside: you may want to learn about the cmd and shlex modules for 
read-eval-print-loop programs :)

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[issue9938] Documentation for argparse interactive use

[Jay T]

New submission from Jay T jayt...@gmail.com:

I want to create a custom interactive shell where I continually do 
parse_args.  Like the following: 
parser = argparse.ArgumentParser() 
command = raw_input() 
while(True): 
  args = parser.parse_args(shlex.split(command)) 
  # Do some magic stuff 
  command = raw_input() 
The problem is that if I give it invalid input, it errors and exits 
with a help message.

I learned from argparse-users group that you can override the exit method like 
the following:

class MyParser(ArgumentParser): 
  def exit(self, status=0, message=None): 
# do whatever you want here 

I would be nice to have this usage documented perhaps along with best practices 
for doing help messages in this scenario.

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assignee: d...@python
components: Documentation
messages: 117287
nosy: d...@python, jayt
priority: normal
severity: normal
status: open
title: Documentation for argparse interactive use
type: feature request
versions: Python 2.7

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[issue9938] Documentation for argparse interactive use

[Steven Bethard]

Changes by Steven Bethard steven.beth...@gmail.com:


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