Add Python docstrings

main.py

@@ -1,4 +1,7 @@
 #!/usr/bin/env python3
+"""
+Parse strategy matrix in GitHub Action.
+"""
 import json
 import os
 from typing import Any
@@ -7,47 +10,24 @@
 
 
 def output(name: str, value: str) -> None:
+    """
+    Write out an GitHub Action output.
+    """
     with open(os.environ["GITHUB_OUTPUT"], "a", encoding="UTF-8") as output_file:
         output_file.write(f"{name}={value}\r\n")
 
 
 def setenv(name: str, value: str) -> None:
+    """
+    Write out an GitHub Action environment variable.
+    """
     with open(os.environ["GITHUB_ENV"], "a", encoding="UTF-8") as output_file:
         output_file.write(f"{name}={value}\r\n")
 
 
-def parse_base_matrix(input_matrix: str) -> dict:
-    matrix = yaml.load(input_matrix, Loader=yaml.loader.BaseLoader)
-    if matrix is None:
-        return {}
-    if not isinstance(matrix, dict):
-        raise TypeError(f"Matrix must be a dict, but {type(matrix)} received.")
-    for variable, values in matrix.items():
-        if not isinstance(variable, str):
-            raise TypeError(
-                f"Matrix variables must be strings, but variable of type "
-                f"{type(variable)} received."
-            )
-        for reserved_name in ("include", "exclude"):
-            if variable == reserved_name:
-                raise ValueError(f"Variable name '{reserved_name}' is reserved.")
-        if not isinstance(values, list):
-            raise TypeError(
-                f"Matrix values must be lists, but {type(values)} received "
-                f"for variable '{variable}'."
-            )
-        for value in values:
-            if not isinstance(value, str):
-                raise TypeError(
-                    f"Each matrix value must be a string, but value of type "
-                    f"{type(values)} received for variable '{variable}'."
-                )
-    return matrix
-
-
 def assert_valid_extra(extra: Any) -> None:
     """
-    Validate strategy include/exclude.
+    Validate strategy matrix include/exclude.
     """
     if not isinstance(extra, list):
         raise TypeError(
@@ -117,19 +97,27 @@ def parse_matrix(input_matrix: str) -> dict:
     """
     # Parse every YAML scalar as a string
     matrix = yaml.load(input_matrix, Loader=yaml.loader.BaseLoader)
-    print(matrix)
 
     assert_valid_matrix(matrix)
 
     return matrix
 
 
-if __name__ == "__main__":
+def main() -> None:
+    """
+    Parse strategy matrix from GitHub Action input ('matrix'), parse and
+    validate it, print it out and set it as output ('matrix') and as
+    environment variable ('MATRIX').
+    """
     matrix = parse_matrix(os.environ["INPUT_MATRIX"])
 
-    print(yaml.dump({"matrix": matrix}))
+    print(yaml.dump({"matrix": matrix}, sort_keys=False))
 
     output_matrix = json.dumps(matrix)
 
     output("matrix", output_matrix)
     setenv("MATRIX", output_matrix)
+
+
+if __name__ == "__main__":
+    main()