Add session 06 on type hints

meetings/2021/session_06_type_annotation_for_less_bugs/.gitignore

+helpers/venv

meetings/2021/session_06_type_annotation_for_less_bugs/README.md

+# Type hints
+
+Type hints are an optional feature introduced in Python 3.5 and
+described in [a multitude of PEPs](https://docs.python.org/3/library/typing.html).
+They allow specifying the type of inputs, outputs and variables
+and can be used by a miriad of tools to help you check if the
+code is self consistent, provide contextual auto-completion,
+among other benefits.
+
+## Static type analysers
+
+Static type analysers ensure that the type of different parts
+of the code match on which types they expect.
+Since types are explicitly stated, IDEs can also use this
+information to provide contextual auto-completion.
+
+There are several tools that provide this feature. The three
+most well known are:
+
+* [mypy](http://mypy-lang.org/), community developed, first on scene and widely used.
+* [pytype](https://github.com/google/pytype) developed at Google (but not officially supported).
+* [pyright](https://github.com/microsoft/pyright) officially supported by Microsoft (written in JavaScript)
+
+All of them provide static code inspection with some differences
+in features and how you interact with it.
+
+## .pyi stub files
+
+Static analysis tools can often also use and in some cases generate
+.pyi files (specified in [PEP 561](https://www.python.org/dev/peps/pep-0561))
+that contain the type hints.
+If you are familiar with C languages, they can be seen as the *header* files,
+providing only the signatures of functions, classes and variables.
+
+Since type hints are still a relatively new feature and not all libraries
+are using it, the python community has setup repositories such as
+[typeshed](https://github.com/python/typeshed) to provide stub files for
+commonly used libraries. These are in turn used by static analysers 
+such as **mypy** to improve type checking and code inspection.
+
+## Common types
+
+* int
+* str
+* bytes
+* float
+* tuple
+* list

meetings/2021/session_06_type_annotation_for_less_bugs/helpers/make_venv.sh

+#!/usr/bin/env sh
+
+python3.9 -m venv helpers/venv
+source helpers/venv/bin/activate
+pip install -r helpers/requirements.txt

meetings/2021/session_06_type_annotation_for_less_bugs/helpers/requirements.txt

+mypy

meetings/2021/session_06_type_annotation_for_less_bugs/sample.py

+# -*- coding: utf-8 -*-
+# Needed for Python >=3.7 <3.10
+from __future__ import annotations
+
+# Types to explore:
+# int, str
+# list, dict, tuple, set
+# class
+# typing.Any
+# typing.Union
+# typing.Optional
+# typing.NewType (aka alias)
+# collections.abc.*
+
+# def multiply(var: annot = default) -> returnval:
+
+
+def main():
+    pass
+
+
+if __name__ == "__main__":
+    main()

meetings/2021/session_06_type_annotation_for_less_bugs/verify.sh

+#!/usr/bin/env sh
+
+set -e
+
+if [ ! -f helpers/venv/bin/activate ]; then
+  ./helpers/make_venv.sh
+fi
+
+source helpers/venv/bin/activate
+
+mypy sample.py