Fixed issue#949

[luojiebin]

Added a way to distinguish between pip installed packages and those from
the system package manager in 'pip list'. Specifically, 'pip list -vv' also
shows the installer of package.

[xavfernandez]

I'm not sure we wan't to keep adding -v for each new column (should we print the license on -vvv then ? ;) ).
Printing the installer in single -v mode might already make sense, or perhaps allow the user to configure somehow the list of columns to show ? Something like pip list --format="columns:pkg,version,installer" ?

[pfmoore]

Yeah, I'm a bit concerned about this too. I don't want to over-generalise just for the sake of it, but adding extra columns isn't really what I'd expect -v to be for.

[luojiebin]

To make it simple and functional. Does it make sense to just show both location and installer of a package when "pip list -v" ?

[luojiebin]

@xavfernandez

pip list --format="columns:pkg,version,installer"

Is this way a little complicated? I guess it's better to keep it as simple as possiple.

[pfmoore]

OK, I'm confused here. The build has failed because a Distribution object has no "installer" attribute, which is correct. How were you planning on getting the installer metadata? You probably want something like Distribution.get_metadata('installer') but you'll need to tidy it up a bit.

Actually, I'm concerned about the scope creep here. As @xavfernandez pointed out, what's to stop someone else asking for another field to be added?

At the end of the day, pip list is a pretty thin wrapper around pkg_resources. At some point we should consider whether it's right to keep adding complexity, and when users should be encouraged to write their own script. After all, pip list -v is little more than

from pkg_resources import working_set
for dist in working_set:
    print(f"{dist.project_name} {dist.version} {dist.location}")

(with a bit of layout added).

[luojiebin]

@pfmoore Thanks. I read the source code and find it can get 'installer' attribute in 'show' command and make a mistake to think package has the 'installer' attribute.

Yes, I agree. It should stop someone else asking for another field to be added, because it will make the 'list' command completed.

Then, how should we deal with issue#949 ?Does it make sense to just show both location and installer of a package when "pip list -v", then stop add more columns and encourage users write their own script. Because install location and installer are importance information of a package. Or we should close issue#949?

[pfmoore]

The comments in #949 note that pip show --verbose <pkg> already shows the installer flag. I'm OK with making pip list -v show both the location and the installer flag, as you suggest, but I'm not actually sure it's needed. I've asked on #949 if what's already available is sufficient.

BTW, I just noticed that get_metadata('installer') raises an exception if there's no installer metadata, so you have to be prepared for that. It's not that it's hard to handle, but it does demonstrate that this change isn't quite as trivial as it first seemed... ;-)

[luojiebin]

@pfmoore Yes, it is not simple. I will think it again. Thanks for advice patiently.

[xavfernandez]

I'm not sure it makes sense to include the installer (and the location, fwiw) in the freeze format.

[luojiebin]

I think it's reasonable to remove installer from freeze format too.

[xavfernandez]

This function should go to pip.utils.packaging

[xavfernandez]

@luojiebin Thanks 👍