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.

As part of the above use-case sometimes versions of the stable constraints need an override with a different (i.e. newer) version. Other software follow the same idea are mr.developer for Python's zc.buildout or mrs-developer for NPM packages.

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Overview

mxdev procedure is:

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

mxdev will not run pip for you!

Installation

pip install mxdev

mxdev >=4.0 needs pip version 23 at minimum to work properly

Quick Start

1. Create mx.ini configuration file:

[settings]
requirements-in = requirements.txt
requirements-out = requirements-mxdev.txt
constraints-out = constraints-mxdev.txt

# Custom variables for reuse
github = git+ssh://git@github.com/

[mypackage]
url = ${settings:github}myorg/mypackage.git
branch = main
extras = test

2. Run mxdev to fetch sources and generate files:

mxdev

3. Install with pip using the generated files:

pip install -r requirements-mxdev.txt

For more examples see the example/ directory.

Configuration

Configuration is done in an INI file (default: mx.ini) using configparser.ExtendedInterpolation syntax.

Settings Section [settings]

The main section must be called [settings], even if kept empty.

I/O Settings

Option	Description	Default
requirements-in	Input requirements file (can be URL). Empty value = generate from INI only	requirements.txt
requirements-out	Output requirements with development sources as -e entries	requirements-mxdev.txt
constraints-out	Output constraints (developed packages commented out)	constraints-mxdev.txt

Behavior Settings

Option	Description	Default
default-target	Target directory for VCS checkouts	./sources
threads	Number of parallel threads for fetching sources	4
smart-threading	Process HTTPS packages serially to avoid overlapping credential prompts (see below)	True
offline	Skip all VCS and HTTP fetches; use cached HTTP content from .mxdev_cache/ (see below)	False
default-install-mode	Default install-mode for packages: editable, fixed, or skip (see below)	editable
default-update	Default update behavior: yes or no	yes
default-use	Default use behavior (when false, sources not checked out)	True

Smart Threading

When smart-threading is enabled (default), mxdev uses a two-phase approach to prevent credential prompts from overlapping:

1. Phase 1: HTTPS packages without pushurl are processed serially (one at a time) to ensure clean, visible credential prompts
2. Phase 2: Remaining packages (SSH, local, HTTPS with pushurl) are processed in parallel for speed

Optimization: HTTPS URLs with pushurl defined are assumed to be read-only/public and processed in parallel, since the pushurl indicates authenticated write access is separate.

This solves the problem where parallel git operations would cause multiple credential prompts to overlap, making it confusing which package needs credentials.

When to disable: Set smart-threading = false if you have git credential helpers configured (e.g., credential cache, credential store) and never see prompts.

Offline Mode and HTTP Caching

When offline mode is enabled (or via -o/--offline flag), mxdev operates without any network access:

1. HTTP Caching: HTTP-referenced requirements/constraints files are automatically cached in .mxdev_cache/ during online mode
2. Offline Usage: In offline mode, mxdev reads from the cache instead of fetching from the network
3. Cache Miss: If a referenced HTTP file is not in the cache, mxdev will error and prompt you to run in online mode first

Example workflow:

# First run in online mode to populate cache
mxdev

# Subsequent runs can be offline (e.g., on airplane, restricted network)
mxdev -o

# Cache persists across runs, enabling true offline development

Cache location: .mxdev_cache/ (automatically added to .gitignore)

When to use offline mode:

• Working without internet access (airplanes, restricted networks)
• Testing configuration changes without re-fetching
• Faster iterations when VCS sources are already checked out

Note: Offline mode tolerates missing source directories (logs warnings), while non-offline mode treats missing sources as fatal errors.

Package Overrides

version-overrides

Override package versions which are already defined in a dependent constraints file. I.e. an upstream constraints.txt contains already somefancypackage==2.0.3. Given that, for some reason (like with my further developed sources), we need version 3.0.0 of the above package.

Then in this section, this can be defined as:

[settings]
version-overrides =
    somefancypackage==3.0.0
    otherpackage==33.12.1

It is possible to add as many overrides as needed. When writing the constraints-out, the new version will be taken into account. If there is a source section defined for the same package, the source will be used and entries here are ignored.

Note: When using uv pip install the version overrides here are not needed, since it supports overrides natively. With uv it is recommended to create an overrides.txt file with the version overrides and use uv pip install --override overrides.txt [..] to install the packages.

ignores

Ignore packages that are already defined in a dependent constraints file. No new version will be provided. This is specifically handy if a package is going to be installed editable from local file system (like -e .), but was already pinned in an upstream constraints file.

This can be defined as:

[settings]
ignores =
    somefancypackage
    otherpackage

main-package

mxdev can handle one Python package as main package directly via ini config. If defined, it will be added as last entry in the resulting requirements out file.

This can be defined as:

[settings]
main-package = -e .[test]

If the main package is defined in a dependent constraint file, its name must be added to ignores.

Advanced Settings

include

Include one or more other INI files.

The included file is read before the main file, so the main file overrides included settings. Included files may include other files. Innermost inclusions are read first.

If an included file is an HTTP-URL, it is loaded from there.

If the included file is a relative path, it is loaded relative to the parent's directory or URL.

Default: empty

directory

mxdev provides a default setting containing the current working directory which can be used inside package or custom sections:

[sectionname]
param = ${settings:directory}/some/path

Custom Variables

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

[settings]
github = git+ssh://git@github.com/
gitlab = git+ssh://git@gitlab.com/

Package Source Sections

Sections other than [settings] can define:

• Package sources: [PACKAGENAME] - VCS sources to checkout and develop
• Hook configuration: [hookname-section] - Settings for mxdev extensions (see EXTENDING.md)

For package sources, the section name is the package name: [PACKAGENAME]

Basic Package Options

Option	Type	Description	Default
url	required	VCS checkout URL	—
vcs	optional	Version control system: git, fs, svn, gitsvn, hg, bzr, darcs	git
branch	optional	Branch name or tag to checkout	main
extras	optional	Comma-separated package extras (e.g., test,dev)	empty
subdirectory	optional	Path to Python package when not in repository root	empty
target	optional	Custom target directory (overrides default-target)	default-target
pushurl	optional	Writable URL(s) for pushes. Supports single URL or multiline list for pushing to multiple remotes. Not applied after initial checkout.	—

VCS Support Status:

• git (stable, tested)
• fs (stable, tested) - local directory pseudo-VCS
• svn, gitsvn, hg, bzr, darcs (unstable, tests need rewrite)

Installation Options

Option	Description	Default
install-mode	editable: Install with -e (development mode) fixed: Install without -e (production/Docker) skip: Only clone, don't install ⚠️ direct is deprecated, use editable	default-install-mode
use	When false, source is not checked out and version not overridden	default-use

Git-Specific Options

Option	Description	Default
depth	Git clone depth (shallow clone). Set GIT_CLONE_DEPTH=1 env var for global default	full clone
submodules	Submodule handling: always, checkout, recursive (see below)	always

Git Submodule Modes

• always (default): Git submodules will always be checked out, updated if already present
• checkout: Submodules only fetched during checkout, existing submodules stay untouched
• recursive: Fetches submodules recursively, results in git clone --recurse-submodules on checkout and submodule update --init --recursive on update

Multiple Push URLs

You can configure a package to push to multiple remotes (e.g., mirroring to GitHub and GitLab):

[my-package]
url = https://github.com/org/repo.git
pushurl =
    git@github.com:org/repo.git
    git@gitlab.com:org/repo.git
    git@bitbucket.org:org/repo.git

When you run git push in the checked-out repository, Git will push to all configured pushurls sequentially.

Note: Multiple pushurls only work with the git VCS type. This mirrors Git's native behavior where a remote can have multiple push URLs.

Usage

Run mxdev (for more options run mxdev --help).

Mxdev will

1. read the configuration from mx.ini,
2. fetch the packages defined in the config file and
3. write a requirements and constraints file.

Now, use the generated requirements and constraints files with i.e. pip install -r requirements-mxdev.txt.

Example Configuration

Example mx.ini

This looks like so:

[settings]
requirements-in = requirements.txt
requirements-out = requirements-mxdev.txt
constraints-out = constraints-mxdev.txt

version-overrides =
    baz.baaz==1.9.32

ignores =
    my.ignoredpackage

# custom variables
github = git+ssh://git@github.com/
mygit = git+ssh://git@git.kup.tirol/

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

[kup.fancyproject]
url = ${settings:mygit}customers/fancycorp/kup.fancyproject.git
branch = fix99
extras = test,baz

More Examples

For comprehensive examples demonstrating all features, see the example/ directory.

Real-World Examples

• "new" plone.org backend
• Conestack

Extending

The functionality of mxdev can be extended by hooks. This is useful to generate additional scripts or files or automate any other setup steps related to mxdev's domain.

See EXTENDING.md for complete documentation on creating mxdev extensions.

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://git@github.com/orga/foo.bar.git@fix-99. Neither it is possible to override inherited version constraints with custom ones.

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. Same is true for version overrides: a new entry is written to the resulting constraints file while the original version is disabled. The configuration is read from a file mx.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 the word "mix".

Misc

The VCS-related code is taken from mr.developer. Thanks to Florian Schulze and Contributors.