Description
What's the problem this feature will solve?
pip currently does not have any mechanism for users to get the result of pip's dependency resolution. This functionality is useful for users to be able to:
- generate something like a "lockfile"
- checking if installing a package would break the existing environment
- checking for dependency conflicts among a set of packages
- (more?)
All these can be performed today, but require installing packages to some environment and introspecting the environment for information. Since all the relevant information is available to pip install at run time, it would be useful to avoid hitting issues with this.
Describe the solution you'd like
#8032 proposes a pip install --dry-run option.
#7819 proposes a pip resolve command.
#1345 has more proposals. :)
There have likely more proposals in the issue tracker that I can't find.
Alternative Solutions
Let other not-pip tooling in the ecosystem provide this functionality to users. This is sub-optimal given that pip's resolver isn't exposed publicly in any way (pip's internals are not to be used like a library).
The most notable example is pip-tools project, which is the current best answer for any user who is seeking this functionality.
Note: This description has been edited by @pradyunsg in April 2020 (see edit history for details), and some really old, outdated comments have been hidden on this issue.