Calculate version number based on pyproject.toml

During `poetry install`, Poetry installs the project as if it were a
package itself. You can then pull the version from the package metadata.
It's a little tricky to get `importlib_metadata` to work with Docker.
You have to remove `--no-root` from the _Dockerfile_ and add
`importlib-metadata` to prod dependencies, and you still might get
errors after that.

python-poetry/poetry#144
python-poetry/poetry#1036

portfolio/__init__.py

@@ -1 +1,16 @@
-__version__ = "0.2.0"
+"""
+Calculate version number based on pyproject.toml.
+---
+During `poetry install`, Poetry installs the project as if it were a package itself.
+You can then pull from the package metadata.
+It's a little tricky to get `importlib_metadata` to work with Docker builds.
+You have to remove `--no-root` from the _Dockerfile_ and move `importlib-metadata`
+to prod dependencies, and you still might get errors after that.
+
+See [poetry#1036](https://github.com/python-poetry/poetry/issues/1036) and
+[poetry#144](https://github.com/python-poetry/poetry/issues/144) for more info.
+"""
+
+from importlib_metadata import version
+
+__version__ = version(__package__)

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "portfolio"
-version = "0.1.0"
+version = "0.3.0"
 description = "Getting Started Testing: pytest edition"
 authors = ["Brendon Smith <br3ndonland@protonmail.com>"]
 license = "MIT"

tests/test_version.py

@@ -2,4 +2,5 @@
 
 
 def test_version():
-    assert __version__ == "0.2.0"
+    """Verify version number in __init__.py."""
+    assert __version__ == "0.3.0"