Add pip inspect command

[sbidoul]

This follows from the discussions in #11223 and #11097. Inspired from pip list and the installation report format.

This is fairly straightforward (although the underlying logic in pip may not be as trivial as it looks at first glance).

Fully open to bike shedding and everything of course.

@pypa/pip-committers if you agree (or don't disagree too much :) I can document it in the same style as #10771, and this can be done fairly quickly.

closes #5261
closes #7967
closes #8008
closes #11223

Example:

{
  "version": "0",
  "pip_version": "22.2.dev0",
  "installed": [
    {
      "metadata": {
        "metadata_version": "2.1",
        "name": "pyparsing",
        "version": "3.0.9",
        "summary": "pyparsing module - Classes and methods to define and execute parsing grammars",
        "description_content_type": "text/x-rst",
        "author_email": "Paul McGuire <ptmcg.gm+pyparsing@gmail.com>",
        "classifier": [
          "Development Status :: 5 - Production/Stable",
          "Intended Audience :: Developers",
          "Intended Audience :: Information Technology",
          "License :: OSI Approved :: MIT License",
          "Operating System :: OS Independent",
          "Programming Language :: Python",
          "Programming Language :: Python :: 3",
          "Programming Language :: Python :: 3.6",
          "Programming Language :: Python :: 3.7",
          "Programming Language :: Python :: 3.8",
          "Programming Language :: Python :: 3.9",
          "Programming Language :: Python :: 3.10",
          "Programming Language :: Python :: 3 :: Only",
          "Programming Language :: Python :: Implementation :: CPython",
          "Programming Language :: Python :: Implementation :: PyPy",
          "Typing :: Typed"
        ],
        "requires_dist": [
          "railroad-diagrams ; extra == \"diagrams\"",
          "jinja2 ; extra == \"diagrams\""
        ],
        "requires_python": ">=3.6.8",
        "project_url": [
          "Homepage, https://github.com/pyparsing/pyparsing/"
        ],
        "provides_extra": [
          "diagrams"
        ],
        "description": "..."
      },
      "metadata_location": "/home/me/.virtualenvs/demoenv/lib/python3.8/site-packages/pyparsing-3.0.9.dist-info",
      "installer": "pip",
      "requested": false
    },
    {
      "metadata": {
        "metadata_version": "2.1",
        "name": "packaging",
        "version": "21.3",
        "platform": [
          "UNKNOWN"
        ],
        "summary": "Core utilities for Python packages",
        "description_content_type": "text/x-rst",
        "home_page": "https://github.com/pypa/packaging",
        "author": "Donald Stufft and individual contributors",
        "author_email": "donald@stufft.io",
        "license": "BSD-2-Clause or Apache-2.0",
        "classifier": [
          "Development Status :: 5 - Production/Stable",
          "Intended Audience :: Developers",
          "License :: OSI Approved :: Apache Software License",
          "License :: OSI Approved :: BSD License",
          "Programming Language :: Python",
          "Programming Language :: Python :: 3",
          "Programming Language :: Python :: 3 :: Only",
          "Programming Language :: Python :: 3.6",
          "Programming Language :: Python :: 3.7",
          "Programming Language :: Python :: 3.8",
          "Programming Language :: Python :: 3.9",
          "Programming Language :: Python :: 3.10",
          "Programming Language :: Python :: Implementation :: CPython",
          "Programming Language :: Python :: Implementation :: PyPy"
        ],
        "requires_dist": [
          "pyparsing (!=3.0.5,>=2.0.2)"
        ],
        "requires_python": ">=3.6",
        "description": "..."
      },
      "metadata_location": "/home/me/.virtualenvs/demoenv/lib/python3.8/site-packages/packaging-21.3.dist-info",
      "installer": "pip",
      "requested": true
    },
    {
      "metadata": {
        "metadata_version": "2.1",
        "name": "pip",
        "version": "22.2.dev0",
        "summary": "The PyPA recommended tool for installing Python packages.",
        "home_page": "https://pip.pypa.io/",
        "author": "The pip developers",
        "author_email": "distutils-sig@python.org",
        "license": "MIT",
        "classifier": [
          "Development Status :: 5 - Production/Stable",
          "Intended Audience :: Developers",
          "License :: OSI Approved :: MIT License",
          "Topic :: Software Development :: Build Tools",
          "Programming Language :: Python",
          "Programming Language :: Python :: 3",
          "Programming Language :: Python :: 3 :: Only",
          "Programming Language :: Python :: 3.7",
          "Programming Language :: Python :: 3.8",
          "Programming Language :: Python :: 3.9",
          "Programming Language :: Python :: 3.10",
          "Programming Language :: Python :: Implementation :: CPython",
          "Programming Language :: Python :: Implementation :: PyPy"
        ],
        "requires_python": ">=3.7",
        "project_url": [
          "Documentation, https://pip.pypa.io",
          "Source, https://github.com/pypa/pip",
          "Changelog, https://pip.pypa.io/en/stable/news/"
        ],
        "description": "..."
      },
      "metadata_location": "/home/me/pip/src/pip.egg-info",
      "direct_url": {
        "url": "file:///home/me/pip/src",
        "dir_info": {
          "editable": true
        }
      }
    }
  ],
  "environment": {
    "implementation_name": "cpython",
    "implementation_version": "3.8.10",
    "os_name": "posix",
    "platform_machine": "x86_64",
    "platform_release": "5.13-generic",
    "platform_system": "Linux",
    "platform_version": "...",
    "python_full_version": "3.8.10",
    "platform_python_implementation": "CPython",
    "python_version": "3.8",
    "sys_platform": "linux"
  }
}

[pradyunsg]

I’m on board, and pleasantly surprised at how quickly you turned this around! We’re having a very active weekend across PyPI and pip. :)

[sbidoul]

I marked this issue as closing the pip show --json issue and siblings. It is not exactly the same but it is easy to use pip inspect and filter out a single distribution out of its result.

@pradyunsg I found where you mentioned pip inspect: #8077 (comment). This pip inspect is not quite what you had in mind back then, I guess.

But then my stance wrt feature request such as include pip-deptree in pip, would be to say we don't want these in pip itself, but that, thanks to pip inspect (this PR) + packaging, it should be quite easy to update such a tool so that

• it does not need to be installed in the target environment (i.e. it can be installed with pipx instead)
• it does not need to access pip internals (as it can call pip inspect to get what is installed and then process it with the packaging library).

Any opinion about that, @pypa/pip-committers ?

[pradyunsg]

I think the whole idea there, is that you shouldn't need to install anything extra, anywhere, to get dependency information in that format.

I think it's a reasonable enhancement to make and being able to accommodate for such needs, around inspecting the installation database and viewing it in different ways, was partly the motivation in suggesting that this have subcommands.

I'm almost certainly in the camp of "let's not back ourselves into a corner with the design choices we make today", but I empathise that it often comes with additional complexity in the initial implementation to design for the extensibility involved.

[pradyunsg]

But, anyway, I'm not married to that idea and making this information available in a manner that other tooling can build off of pip is a good design approach that I'd say we can do more of.

[sbidoul]

I added a test and documentation. This should be ready.

Tentatively adding to 22.2 as it would make sense to announce this together with the installation report, since they are complementary.

[uranusjr]

I wonder if we should commit to this… Versions numbers recorded in documentation likely this generally get stale without being updated.

[sbidoul]

I think its good to give a sense of when we intend the feature to become stable, and I'm motivated to follow this up in the coming month so it's unlikely that I'll forget. So I'd be in favor of keeping it.

[pradyunsg]

And, we're using "likely" to give us some leeway, in case we do miss this deadline in some way. :)