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 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. WeeWX 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.

Generally, we expect WeeWX to be installed in a virtual envirornment, where the names of its modules and packages would not collide with another application. Nevertheless, it is possible that the user would install to the system's sys.exec, and we should be prepared for this.

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:

Note that these will break a lot of code, particularly the renaming of user. Fortunately, all references to the user or schemas packages are dynamic, that is, they are in the form of string options in weewx.conf or skin.conf. The actual instantiation is done by the WeeWX function weeutil.get_object(). This makes it straightforward to maintain backwards compatibility by having get_object() remap references from user to wee_user at runtime. In a similar manner, references to schemas would get remapped to wee_schemas. All of this would be transparent to the user.

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 combine these 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.

The utility subcommand weectl station manages the station configuration file and skins and can set up new user data areas.

Create a new copy of the configuration file, using the copy of weewx.conf in the package data as a template. The user will be prompted for optional values. The default location of the new file will be ~/weewx-data/weewx.conf.

If the configuration file already exists, then an error will be raised.

If they do not already exist, then the skins are also copied over from the package data to the.

The following are set, either implicitly or explicitly.

Optional path to the configuration file. The value for WEEWX_ROOT will be set to its directory.

The default is ~/weewx-data/weewx.conf.

Set the configuration file up to use the given driver.

Default is weewx.drivers.simulator.

Optional path to where the skins will be installed, relative to $WEEWX_ROOT.

Default is skins.

Optional path to where the generated HTML files and plots will be placed, relative to $WEEWX_ROOT.

Default is public_html.

Do not prompt for values. Obtain new values from the command line only.

This command provides an opportunity to reprovision an existing configuration file.

Reconfigure the configuration file to use the given driver.

Default is to use the existing driver.

Optional path to the configuration file.

The default is ~/weewx-data/weewx.conf. If that doesn't exist, then /etc/weewx/weewx.conf will be tried. If that doesn't exist, then /home/weewx/weewx.conf will be tried.

Do not prompt for values. Obtain new values from the command line only.

If necessary, upgrade an existing configuration file. The old version will be saved as a timestamped copy.

Optional path to the configuration file.

The default is ~/weewx-data/weewx.conf. If that doesn't exist, then /etc/weewx/weewx.conf will be tried. If that doesn't exist, then /home/weewx/weewx.conf will be tried.

The skins will be copied over from the package resource location to the resource root ($WEEWX_ROOT). The old version will be saved under a timestamp.

Optional path to the configuration file.

The default is ~/weewx-data/weewx.conf. If that doesn't exist, then /etc/weewx/weewx.conf will be tried. If that doesn't exist, then /home/weewx/weewx.conf will be tried.

# Create a new weewx.conf in ~/weewx-data, using the vantage driver.
weectl station create --driver=weewx.drivers.vantage

# Same as above, but create in the alternative directory ~/alt-dir
weectl station create --driver=weewx.drivers.vantage --config=~/alt-dir/house.conf

# Reconfigure the configuration file in the default area to use a Fine Offset station
weectl station reconfigure --driver=weewx.drivers.fousb

# Upgrade its configuration file
weectl station upgrade

# Upgrade its skins
weectl station upgrade-skins

This subcommand manages daemon files.

Throughout this document, the following definitions are used