feat: Allow automatic execution of code blocks thanks to the `MARKDOW…

…N_EXEC_AUTO` environment variable

Issue-24: #24

docs/usage/index.md

@@ -12,6 +12,14 @@ print("Hello Markdown!")
 The `exec` option will be true for every possible value
 except `0`, `no`, `off` and `false` (case insensitive).
 
+To enable automatic execution of code blocks for specific languages
+(without having to add the `exec="on" option to your code blocks),
+set the `MARKDOWN_EXEC_AUTO` environment variable:
+
+```bash
+MARKDOWN_EXEC_AUTO=python,bash
+```
+
 ## Options summary
 
 As the number of options grew over time,

src/markdown_exec/__init__.py

@@ -8,6 +8,7 @@
 
 from __future__ import annotations
 
+import os
 import re
 from typing import TYPE_CHECKING, Any
 
@@ -26,6 +27,7 @@
 
 __all__: list[str] = ["formatter", "validator"]
 
+MARKDOWN_EXEC_AUTO = [lang.strip() for lang in os.getenv("MARKDOWN_EXEC_AUTO", "").split(",")]
 
 formatters = {
  "bash": _format_bash,
@@ -63,7 +65,7 @@ def validator(
  Returns:
  Success or not.
  """
- exec_value = _to_bool(inputs.pop("exec", "no"))
+ exec_value = language in MARKDOWN_EXEC_AUTO or _to_bool(inputs.pop("exec", "no"))
  if language not in {"tree", "pyodide"} and not exec_value:
  return False
  id_value = inputs.pop("id", "")