## Talk: Edit & Ignore

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 above use-case sometimes versions of the stable constraints need an override with a different (i.e. newer) version.

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

mxdev 2.0 needs pip version 22 at minimum to work properly

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, overridden versions replaced) and requirements (handled packages as editable from sources) are written.

mxdev will not run pip for you!

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

Create an INI file, like mx.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.

If given an empty value mxdev will only generate output from the information given in INI file itself.

Default: requirements.txt

requirements-out

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

constraints-out

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

default-target

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

default-install-mode

Default for install-mode on section, read there for details Allowed values: direct or skip Default: direct

default-update

Default for update on section, read there for details Allowed values: yes or no Default: yes

threads

Number of threads to fetch sources in parallel with. Speeds up fetching from VCS. Default: 4

offline

Do not fetch any sources. Handy if working offline. Default: False

version-overrides

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

ignores

Ignore packages which 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

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.

All other sections are defining the sources to be used.

[PACKAGENAME]

The section name is the package name.

url = URL

The checkout URL of the repository.

The URL is required.

pushurl = URL

Optional a writable URL for pushes can be specified.

If the pushurl is set after initial checkout it is not applied. To apply it remove the repository and checkout again.

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 default target directory configured in main section [settings] default-target = value.

install-mode

There are different modes of pip installation:

skip

Do not install with pip, just clone/update the repository.

direct

Install the package using pip -e PACKAGEPATH. Dependencies are resolved immediately.

Defaults to default mode configured in main section [settings] default-install-mode = value.

submodules

There are 3 different options

always

(default) git submodules will always be checked out, the will be updated if already present

checkout

submodules get 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

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.

This looks like so:

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

version-overrides =
    baz.baaz = 1.9.32

ignores =
    my.ignoredpackage

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

[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

• "new" plone.org backend
• (add more)

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.

Extension configuration settings end up in the mx.ini file. They can be added globally to the settings section, as dedicated config sections or package specific. To avoid naming conflicts, all hook related settings and config sections must be prefixed with a namespace.

It is recommended to use the package name containing the hook as namespace.

This looks like so:

[settings]
myextension-global_setting = 1

[myextension-section]
setting = value

[foo.bar]
myextension-package_setting = 1

The extension is implemented as subclass of mxdev.Hook:

from mxdev import Hook
from mxdev import State

class MyExtension(Hook):

    namespace = None
    """The namespace for this hook."""

    def read(self, state: State) -> None:
        """Gets executed after mxdev read operation."""

    def write(self, state: State) -> None:
        """Gets executed after mxdev write operation."""

The default settings section from the INI file is available at state.configuration.settings. The package configuration is available at state.configuration.packages. Hook related config sections are available at state.configuration.hooks.

The hook must be registered as entry point in the setup.py or setup.cfg of your package:

setup(
    name='myextension',
    ...
    entry_points={
        'mxdev': [
            'hook = myextension:MyExtension',
        ]
    }
)

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/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 mix.

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