How to make pip "dry-run"?

Question

For developing a script that runs pip install it would be usefull to have a --dry-run function.

I came across the --no-install option. But this one is deprecated and on call references this. There are hints to unpack a package only, but I can't find a unpack option in the pip documentation.

Answer 1

Yes - pip should have a dry-run option, to indicate what would happen in a complex situation. It is dangerous when running pip install downgrades packages without asking you. We need some way to ask what would happen if we run pip install -r requirements.txt without laboriously searching thru all the requirements and comparing them to the currently installed ones.

It looks like setup.py used to have a dry-run. Folks are asking for it elsewhere.

Some progress in that direction can be found here:

• Dry Run for Python Pip | BackSlasher
• nvie/pip-tools: A set of tools to keep your pinned Python dependencies fresh.

Update: Activity continues on the official bug related to this: Add `pip install --dry-run` or similar, to get resolution result · Issue #53 · pypa/pip. It is blocked on the development of the dependency resolver, which is nearing completion

Answer 2

It appears you are right, it has been deprecated (ref).

If by trial run you mean testing it out before actually installing a package in a certain place, presumably before a system wide install, then you can simply run it sandboxed using a virtual environment and then simply discard the environment.

virtualenv /tmp/venv; /tmp/venv/bin/pip install flask; rm -rf /tmp/venv  

Not as succinct as using a dry-run argument to pip, but it does the job. Also if you want to do a dry run of a series of package installations, omit the deletion at the end.

In a script you can distil it into a procedure:

#!/bin/bash  TMP_DIR='/tmp/venv'  function dry_run (){     if [ ! -d "$TMP_DIR" ]; then             virtualenv /tmp/venv     fi     /tmp/venv/bin/pip install $1 }  dry_run flask dry_run uwsgi rm -rf $TMP_DIR 

If you want to do a dry run that tests that the new install(s) play well with system wide deployed, then use virtualenv's system-site-packages option.

virtualenv --system-site-packages /tmp/venv; /tmp/venv/bin/pip install flask; rm -rf /tmp/venv