Friendlier error when 3.10 is parsed as float in pyproject.toml

[jamesbraza]

Bug Report

Running mypy with Python 3.10 and python_version in the config file has a few wrong behaviors:

1. It lists mypy must be 3.4 or higher (it should say 3.6)
2. It truncates Python 3.10 to 3.1
3. It outputs a message when there shouldn't be one (you can invoke mypy with Python 3.10)

To Reproduce

Here is a subset of my pyproject.toml:

[tool.mypy]
# SEE: http://mypy.readthedocs.io/en/latest/config_file.html#config-file

# Specifies the Python version used to parse and check the target program.
python_version = 3.10

# Enables PEP 420 style namespace packages.
namespace_packages = true

I invoke mypy via: mypy -p namespacepkg

Expected Behavior

Not to raise this message.

Actual Behavior

pyproject.toml: [mypy]: python_version: Python 3.1 is not supported (must be 3.4 or higher)

Your Environment

• Mypy version used: 0.931
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): see above pyproject.toml
• Python version used: 3.10.2
• Operating system and version: macOS v11.5.1 Big Sur

[JelleZijlstra]

You need to quote it as "3.10", because it's a float! We can probably put a special-case message here to make that clear though.

[jamesbraza]

Changing it to:

# Specifies the Python version used to parse and check the target program.
python_version = "3.10"

Indeed fixes the problem. In hindsight it makes total sense. Yeah maybe a special message would be a good idea, thank you!

[radioactive11]

@hauntsaninja Being a first-time contributor, I would like to work on this issue. Any suggestions on where I can start with?

[nakatomotoi]

@hauntsaninja @jamesbraza
May I work on this issue?

[jamesbraza]

@radioactive11 @nakatomotoi yes either of you can! Just make a fork of mypy, cut a branch, try to implement a solution + add test(s) proving it works (see CONTRIBUTING.md for how to run tests), and open a PR back to mypy's master branch.

[radioactive11]

@jamesbraza Sure!

[radioactive11]

@jamesbraza Should I add a special message when the version mentioned has two decimal digits or a general one?

[JelleZijlstra]

There should be a message specific to this case (though it should also cover 3.11 and other future versions).

[Loriasun]

@hauntsaninja @jamesbraza Hi there, can I still work on this one?