Moved tohttps://hugovk.dev/blog/2021/the-python-3-1-problem/

Or, a variation on the Norway problem

Short version: put quotes around version numbers in YAML.

The Norway problem

TheNorway problem is when you put this in YAML:

countries:-GB-IE-FR-DE-NO

But get this out:

>>>importyaml>>>withopen("countries.yml")asf:...yaml.safe_load(f)...{'countries':['GB','IE','FR','DE',False]}

😱

The Norway fix

Use quotes:

countries:-"GB"-"IE"-"FR"-"DE"-"NO"

>>>withopen("countries.yml")asf:...yaml.safe_load(f)...{'countries':['GB','IE','FR','DE','NO']}

🇳🇴 ✅

The Python 3.1 problem

A similar problem will affect the Python community in October 2021, whenPython 3.10 comes out.

Why?

When3.10 is added to YAML, for example in CI test matrix config, it's interpreted as a float. This:

python-version:[3.6,3.7,3.8,3.9,3.10,pypy3,]

Turns into this:

>>>importyaml>>>withopen("versions.yml")asf:...yaml.safe_load(f)...{'python-version':[3.6,3.7,3.8,3.9,3.1,'pypy3']}

CI failed! It's not2009! Python 3.1 not found!

😱

Relatedly,3.10-dev without quotes works because it's interpreted as a string. But when deleting-dev,3.10 is interpreted as a float.

The Python 3.10 fix

Version numbers are strings, not floats. Use quotes:

python-version:["3.6","3.7","3.8","3.9","3.10","pypy3",]

>>>importyaml>>>withopen("versions.yml")asf:...yaml.safe_load(f)...{'python-version':['3.6','3.7','3.8','3.9','3.10','pypy3']}

🐍 ✅

See also

flake8-2020 is a useful Flake8 plugin to find Python 3.10 and other bugs caused by assumptions about the length of version numbers when usingsys.version andsys.version_info.

Header photo: "zero" byLeo Reynolds is licensed underCC BY-NC-SA 2.0.