[Python-Dev] Feature request: Change a Dependency Package Version During Package Initiation

Dan Ryan dan at danryan.co
Sat May 18 03:18:22 EDT 2019


It probably makes the most sense to formally outline all of the behavioral changes, expectations, and constraints you are asking for as Brett said because dependency and package management are tricky and it's not clear (to me at least) what the request is, what problem is being encountered, and how it is proposed that it be resolved.

First glance makes it sound a bit like the a prerequisite for this request would be allowing multiple versions of the same package to be installed in a given python environment to begin with, or else some runtime hacking of paths would be necessary.  I may be misunderstanding, but that's why a formal approach for something like this might make some sense

Dan Ryan
gh: @techalchemy // e: dan at danryan.co

From: Q [mailto:qiang.fang at zoho.com.cn] 
Sent: Friday, May 17, 2019 10:32 PM
To: Daniel Holth
Cc: Brett Cannon; Python-Dev
Subject: Re: [Python-Dev] Feature request: Change a Dependency Package Version During Package Initiation

Sorry, there is an error in my last post. It's corrected as:
The abaqus python distribution has libA 1.0, the external package to be installed is LibB, which requires libA2.0, and we don't want to change every import in LibB to be import /somewhere/libA2.0, because the source code may have not been provided.


---- 在 星期六, 2019-05-18 10:26:04 Q <qiang.fang at zoho.com.cn> 撰写 ----

>From the viewpoint of the package user, people don't want to change every import to "require a version at runtime". If "set up a python path in a wrapper script" is a better strategy, can you please give an example for the following use case:
The abaqus python distribution has libA 1.0, the external package to be installed is LibB, which requires libA2.0, and we don't want to change every import in LibB to be import libA 1.0, because the source code may have not been provided.
In emacs, you can always advice a command to change its behaviour, which makes it very user friendly, and that what all the following suggestion is about. I have no idea at all how it could be implemented though.
https://github.com/mitsuhiko/multiversion/issues/1
"The work around is to let a version to be set within a package and have that propagate to all modules in that package. For example in the root init.py if I set tonado version to be 2.2.1 then all modules in that package will use tornado 2.2.1 when I import tornado."

---- 在 星期五, 2019-05-17 23:38:55 Daniel Holth <dholth at gmail.com> 撰写 ----



This sounds exactly like what people used to do with eggs. You could have multiple versions of a package on the path as eggs and then require a version at runtime. The approach has problems. Ruby also abandoned a strategy where random app code depends on package management code at runtime.

One better strategy is to set up a python path in a wrapper script.

On Fri, May 17, 2019, 11:27 Brett Cannon <bcannon at gmail.com> wrote:

Thanks for the idea but there are currently no plans to support such a feature. If you would like to see it then you will need to write a PEP with a proof-of-concept to demonstrate how you would expect such a feature to work.

On Fri., May 17, 2019, 07:55 Q via Python-Dev, <python-dev at python.org> wrote:

A lot of the Python code we use in production are used directly as imports in other python
distributions (such as the python comes with the finite element software Abaqus and MSC Marc), many
packages (such as matplotlib, numpy) that may have varying versioned dependencies.

I was wondering if this could be expanded to allow a version to be set within a package and have
that propagate to all modules in that package. For example in the root init.py if I set
multiversion(tornado, 2.2.1) then all modules in that package will use tornado 2.2.1 when I import
tornado.

See a relevant issue on github:
https://github.com/mitsuhiko/multiversion/issues/1

Thank you!
Qiang




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