This page is an attempt to make sense of the dependencies and upgrade paths for weewx. Although weewx (still) has few dependencies itself, the python2/python3 change introduced significant complexity, and the libraries weewx uses (notably python imaging and cheetah) vary widely between platforms.

This is an enumeration of the weewx dependencies for each major operating system release.

# weewx_x.y.z-n_all.deb
#
# required
apt-get install python-configobj
apt-get install python-pil
apt-get install python-cheetah
apt-get install python-usb
apt-get install python-serial
# optional
apt-get install python-ephem
apt-get install mariadb-client
apt-get install python-mysqldb
# weewx
apt-get install weewx

# python3-weewx_x.y.z-n_all.deb
#
# required
apt-get install python3-configobj
apt-get install python3-pil
apt-get install python3-cheetah
apt-get install python3-usb
apt-get install python3-serial
# optional
apt-get install python3-ephem
apt-get install mariadb-client
apt-get install python3-mysqldb
# weewx
apt-get install python3-weewx

# weewx_x.y.z-n_all.deb
#
# required
apt-get install python-configobj
apt-get install python-pil
 OR apt-get install python-imaging
apt-get install python-cheetah
apt-get install python-usb
apt-get install python-serial
# optional
apt-get install python-ephem
apt-get install mysql-client
apt-get install python-mysqldb
# weewx
apt-get install weewx

# no deb package
#
# required
apt-get install python3-configobj
apt-get install python3-pil
apt-get install python3-usb
apt-get install python3-serial
pip3 install cheetah3
# optional
apt-get install python3-ephem
apt-get install mysql-client
apt-get install python3-mysqldb
# weewx
python3 setup.py install

# weewx_x.y.z-n_all.deb
#
# required
apt-get install python-configobj
apt-get install python-pil
 OR apt-get install python-imaging
apt-get install python-cheetah
apt-get install python-usb
apt-get install python-serial
# optional
apt-get install python-dev
apt-get install python-pip
pip install pyephem
apt-get install mysql-client
apt-get install python-mysqldb
# weewx
apt-get install weewx

# no deb package
#
# required
# optional
# weewx
python3 setup.py install

# weewx_x.y.z-n_all.deb
#
# required
apt-get install python-configobj
apt-get install python-pil
 OR apt-get install python-imaging
apt-get install python-cheetah
apt-get install python-usb
apt-get install python-serial
# optional
apt-get install python-dev
apt-get install python-pip
pip install pyephem
apt-get install mysql-client
apt-get install python-mysqldb
# weewx
apt-get install weewx

# no deb package
#
# required
# optional
# weewx
python3 setup.py install

# no rpm package
#
# required
pip2 install configobj
pip2 install pil
pip2 install cheetah
pip2 install pyusb
pip2 install pyserial
# optional
pip2 install pyephem
pip2 install mysqlclient
# weewx
python2 setup.py install

# weewx-x.y.z-n.el8.noarch.rpm
#
# required for cheetah
dnf install epel-release
# required
dnf install python3-configobj
dnf install python3-pillow
dnf install python3-cheetah
dnf install python3-pyusb
dnf install python3-pyserial
# optional
pip3 install pyephem
dnf install python3-pymysql
# weewx
dnf install weewx

# weewx-x.y.z-n.el7.noarch.rpm
#
# required
yum install python-configobj
yum install python-pillow
yum install python-cheetah
yum install pyusb
yum install pyserial
# optional
yum install python-setuptools
easy_install install pyephem
yum install mysql-client
yum install python-mysqldb
# weewx
yum install weewx

# no rpm package
#
# required
pip3 install configobj
pip3 install pil
pip3 install cheetah3
pip3 install pyusb
pip3 install pyserial
# optional
pip3 install ephem
yum install mysql-client
pip3 install mysqldb
# weewx
python3 setup.py install

This is an enumeration of the upgrade paths for weewx, for various operating system packages.

• As of weewx 4, the python2 weewx should be called python-weewx and the python3 package should be called python3-weewx.
• The python3-weewx package will be supported only for debian10 and later, since the python3 packages on which weewx depends are not available in a standard debian9, debian8, or debian7 distribution. (It might be possible to hack that using backports, but that is left as an exercise to the reader)
• The packages python-weewx and python3-weewx cannot co-exist, since they both live in /usr/share/weewx. They differ only by
  • the contents of /etc/default/weewx
  • the Depends in the debian/control file
• The package python-weewx replaces weewx.
• The package python3-weewx replaces weewx.
• The weewx package has been marked as squeeze in the apt repository.
• The python-weewx package should be marked as squeeze in the apt repository.
• The python3-weewx package should be marked as buster in the apt repository.
• If a user specifies or stays on the squeeze release, then that user should continue to use python2.
• If a user specifies or changes to the buster release, then that user should get python3.

• When I put all of the packages into a single control file, I get three packages: weewx, python-weewx, and python3-weewx. Only the weewx package gets all of the actual files, and the dependencies are not right.
• When I do the transitional package configuration, with weewx and python-weewx in one control and weewx and python3-weewx in another control, I get two .deb files for each control.
• When using dh-python, it runs, but it munges the shebang. So for now, sticking with home-grown install target and binary overrides, with two separate invocations of debbuild - one for python-weewx and one for python3-weewx
• Must ensure that any wee_* invocations in the postinst use /usr/bin/wee_* not /usr/share/wee_*.
• Since the postinst invokes wee_config, we might have to make python-config part of the Pre-Depends. But debian docs say pretty strongly to not use Pre-Depends unless absolutely necessary.

• create package weewx with filename python-weewx for python2, associated with distribution squeeze
• create package weewx with filename python3-weewx for python3, associated with distribution buster
• two repositories now, one for squeeze and one for buster (still using aptly to manage the repos)

python-weewx and python3-weewx are actual packages, and weewx is a virtual package. To do this, python-weewx and python3-weewx each have a Provides in the control. Unfortunately this does not fix the problem of using weewx to install - you cannot do apt-get install weewx, but must do apt-get install python-weewx.

Would it be possible to use update-alternatives to switch between python2 and python3?

Basically, the solution is to define a binary dummy package with the same name as the old package in the control file of the new package. The new source package takes over the binary dummy package, and the old source package, which is then binaryless, will be cleaned up by rene, an archive cleanup tool. https://wiki.debian.org/RenamingPackages

This gets the apt-get install weewx to work, since we make weewx have a Depends on python-weewx and python3-weewx. Requires two separate control files.

However, we do not want the transition package to be cleaned up.

Create a single package called weewx. In debian/control, make the Depends smart - it should default to python3 and associated packages, but if any of those fail or are not available, it falls back to the python and associated packages.

Is this even possible? A quick look at the syntax for Depends indicates no. Although you can do a conditional dependency for a single package (e.g., python-pillow | python-pil), you cannot do combined boolean logic. We would need something like (python3 && python3-pil && python3-configobj && python3-cheetah) || (python && (python-pillow | python-pil) && python-configobj && python-cheetah)

There would be two apt repositories. The squeeze repository would have the python-weewx package. The buster repository would have the python3-weewx package.

Users who upgrade from weewx3 to weewx4, but continue with python2, do not have to change their apt configuration.

Users who do a new install with python2 would use this:

deb [arch=all] http://weewx.com/apt/ squeeze main

Users who do a new install with python3 would use this (only on debian10 or later):

deb [arch=all] http://weewx.com/apt/ buster main

• As of weewx 4, the python2 package is el7 and the python3 package is el8. This reflects the python support in the 7 and 8 releases of the operating system.

# how to put the same package into different apt repos as different distributions
https://groups.google.com/forum/#!topic/aptly-discuss/YTLXLUqBbFo