Mixed development source packages on top of stable constraints using pip

mxdev [mɪks dɛv] is a utility that makes it easy to work with Python projects containing lots of packages, of which you only want to develop some.

It builds on top of the idea to have stable version constraints and then develop from a VCS on top of it.

Other software following the same idea are mr.developer for Python's zc.buildout or mrs-developer for NPM packages.

Overview

mxdev procedure is:

1. Configuration is read,
2. Requirements and constraints (given in configuration) are read.
3. Sources from VCS are fetched into a target directory,
4. Modified constraints (handled packages commented)/ requirements (handled packages as editable from sources) are written.

mxdev will not run pip for you!

Configuration

Given a requirements.txt (or similar named) file which itself references a constraints.txt file inside.

Create an INI file, like sources.ini in configparser.ExtendedInterpolation syntax.

The main section must be called [settings], even if kept empty. In the main sections the input and output files are defined.

requirements-in

Main requirements file to start with. This can be an URL too. Default: requirements.txt

requirements-out

Output of the combined requirements including development sources to be used later with pip install. Default: requirements-dev.txt

constraints-out

Output of the combined constraints. Default: constraints-dev.txt

target

Target directory for sources from VCS. Default: ./sources

Additional, custom variables can be defined as key = value pair. Those can be referenced in other values as ${settings:key} and will be expanded there.

Subsequent sections are defining the sources.

[PACKAGENAME]

The section name is the package name.

url = URL

the URL to the source in VCS and must follow the pip install editable format. Attention, this differs from the format one copies from Github/Gitlab, etc. The URL is required.

branch = BRANCHNAME_OR_TAG

the branch name or tag to checkout. Defaults to main.

extras = EXTRA1,EXTRA2

Package extras to install. Default empty.

subdirectory = SUBPATH

For specifying the path to the Python package, when it is not in the root of the VCS directory. Default empty.

target

Target directory for source from this section. Default to target directory configured in main section [settings] target = value.

Usage

Run mxdev -c sources.ini.

Now use the generated requirements and constrainst files with pip install -r NEW_REQUIREMENTS_FILENAME.txt.

Example Configuration

This looks like so:

[settings]
requirements-in = requirements-infile.txt
requirements-out = requirements-outfile.txt
contraints-out = constraints-outfile.txt

# custom variables
github = git+ssh://[email protected]/

[foo.bar]
url = ${settings:github}orga/foo.bar.git
branch = fix99
extras = test,baz

Rationale

Problem

There is a constraint file like -c constraints.txt with a package foo.bar with a version pin. Then it is not possible to install this package in a requirements file editable like -r requirements.txt with -e git+ssh://[email protected]/orga/[email protected].

Idea

A pre-processor fetches (as this can be an URL) and expands all -c SOMEOTHER_FILE_OR_URL and -r SOMEOTHER_FILE_OR_URL files into one, filtering out all packages given in a configuration file. For each of those packages a -e ... entry is generated instead and written to a new TARGET.txt. The configuration is written in a file sources.ini in ExtendedInterpolation INI syntax (YAML would be nice, but the package must have as less dependencies as possible to other packages).

Trivia

Mx (generally pronounced like mix [mɪks], or [məks] in the UK) is meant to be a gender-neutral alternative to the titles Mr. and Ms. but also associates with mix.