Make it possible to freeze requirements without installing the packages

[hickford]

I'm writing a Python app to deploy on Heroku. Per Heroku's guide, I need to list package requirements in a Pip requirements.txt file. They suggest installing the packages locally, then running pip freeze > requirements.txt.

However, one of the packages I want to use in deployment on Heroku can't be installed locally. It's incompatible with my operating system.

So how do I write a requirements.txt including this package suitable for Heroku?

The only way I can think of is to write it by hand - but this would be tedious, because the package in question has dependencies of its own. Besides, this defeats the convenience of pip.

If this isn't possible in pip, I think it should be possible. This is a real world use case and Bundler can do it (example below).

---

When deploying Ruby apps to Heroku, Bundler makes this easy. In my Gemfile I write

gem "pg", :group => :production
gem "sqlite3", :group => :development

The command bundle install then writes a frozen version list Gemfile.lock (analogous to requirements.txt). It doesn't install the packages listed under the 'production' group, but it still freezes a consistent list of versioned packages.

Example: Gemfile and Gemfile.lock

[sigmavirus24]

@matt-hickford the answer is in that question on StackOverflow, in more than one comment/answer.

[qwcode]

generally speaking, if you need different requirements for different environments, then maintain 2 requirements files.
you can minimize the redundancy, by using the the recursive feature:
http://www.pip-installer.org/en/latest/requirements.html#recursive-requirements

if you want to discuss solutions with pip users, feel free to use the pip mailing list.
https://groups.google.com/forum/?hl=en&fromgroups#!forum/python-virtualenv

I'm closing, since this is not a bug or feature request.

[hickford]

Hi Marcus. Sorry, my Stack Overflow question I copied wasn't very clear. My feature request concerns the second part of question - how to write the requirements.txt for Heroku, when it's impossible to install one of the packages locally (because of platform differences).

I've edited the issue description above. If it makes sense, please re-open the issue. Thanks for your patience.

[qwcode]

ok, so a feature request to allow pip to generate an exhaustive requirements file for what pip would install (into a clean environment), given some set of top-level requirements. I can't think of a way to do that now in pip, unless I'm missing something. so I'm leaving the issue open.

[dstufft]

Closing this, I believe that this use case is best solved by pip-compile from pip-tools.