Fix README example and add test to run python-code example in CI (#38)

Fix incorrect example in README, and add missing test that ensures that python-code example in README executes without error.

Author: leifdenby

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add test to check python codeblocks in README keep working as code changes
+  [\#38](https://github.com/mllam/weather-model-graphs/pull/38) @leifdenby
+
 - Add coords_crs and graph_crs arguments to allow for using lat-lons coordinates
   or other CRSs as input. These are then converted to the specific CRS used when
   constructing the graph.
@@ -25,6 +28,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix crash when trying to create flat multiscale graphs with >= 3 levels
   [\#41](https://github.com/mllam/weather-model-graphs/pull/41), @joeloskarsson
 
+- Fix example in README
+  [\#38](https://github.com/mllam/weather-model-graphs/pull/38) @leifdenby
+
 ### Maintenance
 
 - Update github CI actions, including pre-commit action to fix caching issue

README.md

@@ -78,11 +78,14 @@ import numpy as np
 import weather_model_graphs as wmg
 
 # define your (x,y) grid coodinates
-xy_grid = np.meshgrid(np.linspace(0, 1, 32), np.linspace(0, 1, 32))
-xy_grid = np.stack(xy_grid, axis=0)
+xs, ys = np.meshgrid(np.linspace(0, 1, 32), np.linspace(0, 1, 32))
+coords = np.stack([xs.flatten(), ys.flatten()], axis=-1)
 
 # create the full graph
-graph = wmg.create.archetype.create_keisler_graph(xy_grid=xy_grid)
+graph = wmg.create.archetype.create_keisler_graph(
+    coords=coords,
+    mesh_node_distance=1.0/16 # use half the grid spacing for mesh nodes
+)
 
 # split the graph by component
 graph_components = wmg.split_graph_by_edge_attribute(graph=graph, attr='component')

src/weather_model_graphs/create/mesh/kinds/flat.py

@@ -112,4 +112,12 @@ def create_flat_singlescale_mesh_graph(xy, mesh_node_distance: float):
     nx = int(range_x / mesh_node_distance)
     ny = int(range_y / mesh_node_distance)
 
+    if nx == 0 or ny == 0:
+        raise ValueError(
+            "The given `mesh_node_distance` is too large for the provided coordinates. "
+            f"Got mesh_node_distance={mesh_node_distance}, but the x-range is {range_x} "
+            f"and y-range is {range_y}. Maybe you want to decrease the `mesh_node_distance`"
+            " so that the mesh nodes are spaced closer together?"
+        )
+
     return mesh_graph.create_single_level_2d_mesh_graph(xy=xy, nx=nx, ny=ny)

tests/test_readme.py

@@ -0,0 +1,21 @@
+import re
+from pathlib import Path
+
+import pytest
+
+
+def _parse_readme_examples():
+    lines = open(Path(__file__).parent.parent / "README.md").read().splitlines()
+
+    # use regex to find all python code blocks
+    code_blocks = re.findall(r"```python(.*?)```", "\n".join(lines), re.DOTALL)
+
+    return code_blocks
+
+
+@pytest.mark.parametrize("codeblock_example", _parse_readme_examples())
+def test_readme_example(codeblock_example: str):
+    """
+    Check that execution of the python code block in the README does not raise an exception.
+    """
+    exec(codeblock_example)