Python scripts: Use PDM and virtualenv to manage dependencies

PDM and virtualenv are tools to manage installation of Python modules
not included in the Python Standard Library. Usage:

1. Install Pipx (e.g. `brew install pipx`) - https://pipx.pypa.io/
2. Use Pipx to install PDM (`pipx install pdm`).
3. Run `pdm install` in MuseScore's root directory.

The final command creates a virtual environment (.venv folder) and
installs the dependencies mentioned in MuseScore's pyproject.toml.

See #23198 for details.

Author: shoogle

.gitignore

@@ -68,3 +68,9 @@ VERSION
 temp_*
 
 *.local.cmake
+
+# Python
+__pycache__/
+*.pyc
+.venv/
+.pdm-python

pdm.lock

@@ -0,0 +1,16 @@
+[project]
+description = "Python scripts for MuseScore Studio development."
+readme = "https://github.com/musescore/MuseScore/wiki"
+requires-python = ">=3.9"
+dependencies = [
+    "requests>=2.32.3",
+]
+
+# Useful PDM commands:
+# --------------------
+# pdm install                   Install all dependencies into a virtual environment (venv).
+# pdm run <script>              Run a Python script with access to venv.
+# pdm add <package>             Add new dependency on a PyPi package.
+# pdm venv remove in-project    Remove the venv (e.g. to test installation from scratch).
+[tool.pdm]
+distribution = false

pyproject.toml

@@ -4,6 +4,25 @@
 def eprint(*args, **kwargs):
     print(*args, **kwargs, file=sys.stderr)
 
+if __name__ == '__main__' and sys.prefix == sys.base_prefix:
+    # Not running inside a virtual environment. Let's try to load one.
+    import os
+    old_dir = os.path.realpath(__file__)
+    new_dir, script_name = os.path.split(old_dir)
+    rel_pyi = r'.venv\Scripts\python.exe' if sys.platform == 'win32' else '.venv/bin/python'
+    while new_dir != old_dir:
+        abs_pyi = os.path.join(new_dir, rel_pyi)
+        if os.access(abs_pyi, os.X_OK):
+            eprint(f'{script_name}: Loading virtual environment:\n  {abs_pyi}')
+            if sys.platform == 'win32':
+                import subprocess
+                raise SystemExit(subprocess.run([abs_pyi, *sys.argv]).returncode)
+            os.execl(abs_pyi, abs_pyi, *sys.argv)
+        old_dir = new_dir
+        new_dir = os.path.dirname(new_dir)
+    eprint(f'{script_name}: Not running inside a virtual environment.')
+    del old_dir, new_dir, rel_pyi, abs_pyi, script_name
+
 import locale
 if locale.getpreferredencoding().lower() != 'utf-8':
     encoding = locale.getpreferredencoding()