Note to rebase on #346 which should be merged first.

Spaces after comma and semicolon are not just for readability. They make JSON compatible with YAML 1.0.

This is not the right place for the design discussion. Lets continue it on the bug tracker.

This is not the right place for the design discussion. Lets continue it on the bug tracker.

@serhiy-storchaka and @Haypo I updated bpo-29636 with a summary of the design discussion thus far.

I propose continuing this pull request with only --indent and --no-indent. If we end up reaching consensus to add --compact, that can be added in the future. I think it would fit in nicely alongside --indent and --no-indent. In other words, it's not pressing to decide on --compact right now.

#346 has been merged and this PR rebased.

@serhiy-storchaka, @berkerpeksag, @methane and @Haypo: open for review. No more outstanding changes on my end.

@dhimmel Please add NEWS entry.

Thanks @methane for ba16891 which merges in the changes from #5315 (dict order guaranteed as of Python 3.7).

I'll get working on the NEWS entry.

Ready from my end.

As of b8fee34, --help prints the following message:

usage: python -m json.tool [-h] [--sort-keys]
                           [--indent INDENT | --tab | --no-indent | --compact]
                           [infile] [outfile]

A simple command line interface for json module to validate and pretty-print
JSON objects.

positional arguments:
  infile           a JSON file to be validated or pretty-printed
  outfile          write the output of infile to outfile

optional arguments:
  -h, --help       show this help message and exit
  --sort-keys      sort the output of dictionaries by key
  --indent INDENT  separate items with newlines and use this number of spaces
                   for indentation
  --tab            separate items with newlines and use tabs for indentation
  --no-indent      separate items with spaces rather than newlines
  --compact        suppress all whitespace separation (most compact)

What if pass conflicting options? --indent=4 and --tab? --indent=4 and --compact?

What if pass conflicting options? --indent=4 and --tab? --indent=4 and --compact?

The intention is to disallow users from passing multiple whitespace options with argparse's add_mutually_exclusive_group. The implementation will, in most cases, detect and raise an error if multiple whitespace arguments are provided. However, there is an argparse issue (bpo-18943) where mutual exclusivity is not enforced when --indent=4 is specified (since 4 is default).

For example, --compact --tab or --indent=3 --compact or --indent=4 --compact --tab will all throw errors of the form:

python -m json.tool: error: argument --tab: not allowed with argument --compact

--indent=4 --compact (or --indent=4 --tab) does not throw an error. In the case that --indent=4 is specified with --compact, --tab, or no-indent, the later will take precedent.

I hope this feature can be merged ASAP, it's really helpful as a cross-platform command line utility.

I hope this feature can be merged ASAP

@mya12321 the most effective way for you to support this PR would be to chime in on the issue. At present, I think there is some hesitancy to add additional arguments, so if you explain your use case that may be helpful. But as far as I understand, this discussion should go on the bug tracker and not on GitHub.

Would you resolve the conflict?

Well done @dhimmel and thanks for your tenacity!