This document discusses the goals and design decisions for WeeWX Version 5.

Complete WeeWX install, including dependencies, using pip.

No root privileges required to install and manage WeeWX. However, the operating system may require privileges in order to install daemon files and to access hardware.

Future-proof the install. Right now, we depend heavily on custom commands in setup.py. However, the imperative approach of setup.py is being phased out in favor of a more declarative approach, using pyproject.toml (see PEP 621 and PEP 631). As an alternative, we could use setup.cfg, but it's clear that pyproject.toml is the future.

Python 3.7 or greater. Python 3.7 was released over four years ago (on 27 June 2018), so it should be ubiquitous by now. Python 3.7 is necessary to support importing resources. Note that a backport of importlib.resources is available for earlier versions of Python, so we may be able to relax this restriction and allow Python 3.6. Version 5 will use f-strings, so Python 3.5 cannot be supported.

Support for Python 2.7 will be dropped. All references to six and other compatibility shims will be removed.

Stretch goal: introduce asynchronous drivers, which would allow more than one driver to be active at the same time. This feature would probably involve lots of breaking changes, but it would be a lot more elegant than the present pattern of using a WeeWX service to add data to the data pipeline.

The old distutils approach used by previous versions of WeeWX supported a data_files option that could be used to install miscellaneous resources, such as documentation or configuration files, into a final installation target such as /home/weewx.

However, option data_files is being deprecated for a variety of reasons (see this post for a summary). Instead, data resources must now be included as "package data", that is, as part of a Python package. Like any other package, package data includes an __init__.py file, but unlike regular packages, it can include non-code resources.

That means, once installed, these non-code resources will live deep in the target site-packages directory, where they are difficult to find and even more difficult to modify.

Furthermore, package data must be regarded as "read only". For example, it is possible that WeeWX could be installed as a zipfile or Python egg, so, even if a user was willing to find the data resources deep in site-packages somewhere, s/he still could not edit them.

These are the non-code resources that are used in WeeWX and where they will be located as package data:

Previously, we used /home/weewx as the destination for user data, but it requires root access in order to set up. With Version 5, the default area becomes ~/weewx-data in the user's home directory. However, /home/weewx can continue to be used by older installations.

Because pip no longer allows free access to the operating system, these user data cannot be set up by pip. Instead, they must be copied into place using a new tool, weectl.

All of this means that installing WeeWX becomes a two-step process:

• Install using pip. This installs the code base and package data into the Python library.

• Copy package data out of the Python library to a "user data" area using weectl.

See the companion document pip install strategies for all the various way pip and its allies can be used to install WeeWX.

With Version 5, the default area for user data is ~/weewx-data, which allows WeeWX to be installed entirely without root privileges.

The directory /home/weewx served this purpose in previous versions of WeeWX and, indeed, it can continue to be used by just specifying the location /home/weewx/weewx.conf when using the tool weectl. Note that in the past /home/weewx also held WeeWX code in the bin subdirectory, which, starting with V5, will no longer be used. With V5, all source code lives within the Python environment.

There are many tools that were considered to manage the Python distribution build process including setuptools, pdm, flit, and poetry. We have chosen poetry. It is mature, simple to use, depends on pyproject.toml, and very popular. Poetry can also be used to do an in situ install, but that's not the intended use case. Most users will use pip.

The ubiquitous setuptools was considered, but poetry is easier to use and its implementation of pyproject.toml is more mature. NB: this only affects the distribution build process. Either way, pip is used to install.

Applications will be invoked using an entry point. This is a small shim, installed by pip, which invokes a function within a module or package.

Most packages used by WeeWX already start with the prefix wee_, which is a reasonable claim to a namespace. However, there are two problem areas: user and schemas. Renaming them would break a lot of code, particularly the renaming of user.

However, the recommended install method is to use pip with the --user flag, which will cause WeeWX to be installed in the user's home directory, where user and schema are unlikely to compete with other, unrelated, packages.

Through the years, WeeWX has built up an extensive ecosystem of 3rd party extensions. It is essential that we not lose backwards compatibility with them. For this reason, they should continue to be installed directly into the target installation directories, and not indirectly through package resources.

Presently, we have 7 different utilities. Version 5 will start the process of combining them into one command called, simply, weectl, with different subcommands. By having a single application, we make it easier to find the appropriate command: the user can simply run weectl --help.

Version 5 will offer these subcommands:

weectl station create
weectl station reconfigure
weectl station upgrade
weectl extension list
weectl extension install
weectl extension uninstall

# Create a new user data area in ~/weewx-data (the default)
weectl station create
# Upgrade config file, docs, examples, and daemon utility files in ~/weewx-data.
# Skins will be untouched
weectl station upgrade
# Upgrade the config file only
weectl statioin upgrade --what config
# Upgrade the skins only
weectl station upgrade --what skins

# Install the Windy extension:
weectl extension install https://github.com/matthewwall/weewx-windy/archive/master.zip

Throughout this document, the following definitions are used