Abandon python 2

[Changaco]

Python 2.7 is in its last year, it's time for Liberapay to finally make the jump to Python 3.6.

[Changaco]

This StackOverflow answer suggests that it might be as simple as running this single command: aws elasticbeanstalk update-environment --solution-stack-name "64bit Amazon Linux 2018.03 v2.8.0 running Python 3.6" --environment-name "liberapay" --region "eu-west-1".

However it appears that Liberapay isn't ready for that yet because trying to run Liberapay with Python 3.6 locally fails.

[Changaco]

I'm going to attempt the switch. 🤞

[Changaco]

The compilation of libsass failed:

Building wheel for libsass (setup.py): started
Building wheel for libsass (setup.py): finished with status 'error'
Complete output from command /opt/python/run/venv/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-hs41kqva/libsass/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" bdist_wheel -d /tmp/pip-wheel-x9n7apc6 --python-tag cp36:
running bdist_wheel
running build
running build_py
creating build
creating build/lib.linux-x86_64-3.6
copying sass.py -> build/lib.linux-x86_64-3.6
copying sassc.py -> build/lib.linux-x86_64-3.6
copying sasstests.py -> build/lib.linux-x86_64-3.6
creating build/lib.linux-x86_64-3.6/sassutils
copying sassutils/distutils.py -> build/lib.linux-x86_64-3.6/sassutils
copying sassutils/__init__.py -> build/lib.linux-x86_64-3.6/sassutils
copying sassutils/builder.py -> build/lib.linux-x86_64-3.6/sassutils
copying sassutils/wsgi.py -> build/lib.linux-x86_64-3.6/sassutils
running build_ext
building '_sass' extension
creating build/temp.linux-x86_64-3.6
creating build/temp.linux-x86_64-3.6/libsass
creating build/temp.linux-x86_64-3.6/libsass/src
gcc -pthread -Wno-unused-result -Wsign-compare -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I./libsass/include -I/usr/include/python3.6m -c pysass.cpp -o build/temp.linux-x86_64-3.6/pysass.o -c -O3 -fPIC -std=c++0x -Wall -Wno-parentheses -Werror=switch -DLIBSASS_VERSION="3.3.5"
gcc: error trying to exec 'cc1plus': execvp: No such file or directory
error: command 'gcc' failed with exit status 1

----------------------------------------
Failed building wheel for libsass
Running setup.py clean for libsass

[Changaco]

Now it's failing on the parsing of the Japanese translations file. 😕

[Changaco]

Liberapay is now running on Python 3.6.7 🕺

We had 25 minutes of downtime, but glancing at the logs it doesn't look like any human user was affected.

More problematic: requests containing non-ASCII chars in the path are failing completely (e.g. https://liberapay.com/%C3%A9).

[Changaco]

I thought upgrading Pando would be enough to fix that Unicode issue, but it's not: AspenWeb/pando.py#587.

Edit: almost fixed in #1412.

Edit 2: finally fixed in #1416.