Programmatically comparing Python version strings

python/comparing-version-numbers.md

@@ -0,0 +1,49 @@
+# Programmatically comparing Python version strings
+
+I found myself wanting to compare the version numbers `0.63.1`, `1.0` and the `1.0a13` in Python code, in order to mark a `pytest` test as skipped if the installed version of Datasette was pre-1.0.
+
+This is very slightly tricky, because `1.0` is a higher version than `1.0a13` but comparing it based on string comparison or a `tuple` of components split by `.` would give the wrong result.
+
+It turns out the [packaging.version](https://packaging.pypa.io/en/stable/version.html) Python package solves this exact problem:
+
+```bash
+python -m pip install packaging
+```
+Then:
+```python
+from packaging.version import parse
+
+v_1_0 = parse("1.0")
+v_1_0a13 = parse("1.0a13")
+v_0631 = parse("0.63.1")
+```
+And some comparisons:
+```pycon
+>>> v_1_0 > v_1_0a13
+True
+>>> v_1_0 < v_1_0a13
+False
+>>> v_0631 < v_1_0
+True
+>>> v_0631 < v_1_0a13
+True
+```
+
+## Using this with pytest
+
+Here's how I used this to decorate a `pytest` test so it would only run on versions of Datasette more recent than `1.0a13`:
+```python
+from datasette import version
+from packaging.version import parse
+import pytest
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(
+    parse(version.__version__) < parse("1.0a13"),
+    reason="uses row_actions() plugin hook",
+)
+async def test_row_actions():
+    # ...
+```
+Full [example test here](https://github.com/datasette/datasette-enrichments/blob/c0deca1481d1c1e4b4d6a5802d4252adc3d84fb8/tests/test_enrichments.py#L153-L180).