Change default version command - Enhancement #263

Author: NilayGanvit

.gitignore

@@ -5,6 +5,7 @@
 /env*/
 /python-manager/
 /pythons/
+/.venv/
 
 # Can't seem to stop WiX from creating this directory...
 /src/pymanager/obj

src/manage/commands.py

@@ -85,6 +85,9 @@
      r"Equivalent to -V:PythonCore\3!B!<VERSION>!W!. The version must begin " +
      "with a '3', platform overrides are permitted, and regular Python " +
      "options may follow. The runtime will be installed if needed."),
+     (f"{EXE_NAME} default !B!<TAG>!W!\n",
+     "Set the default Python version to use when no specific version is " +
+     "requested. Use without !B!<TAG>!W! to show the current default."),
 ]
 
 
@@ -216,6 +219,10 @@ def execute(self):
         "help": ("show_help", True), # nested to avoid conflict with command
     },
 
+    "default": {
+        "help": ("show_help", True), # nested to avoid conflict with command
+    },
+
     "**first_run": {
         "explicit": ("explicit", True),
     },
@@ -260,6 +267,9 @@ def execute(self):
         "enable_entrypoints": (config_bool, None),
     },
 
+    "default": {
+    },
+
     "first_run": {
         "enabled": (config_bool, None, "env"),
         "explicit": (config_bool, None),
@@ -1022,6 +1032,34 @@ def execute(self):
                 os.startfile(HELP_URL)
 
 
+class DefaultCommand(BaseCommand):
+    CMD = "default"
+    HELP_LINE = ("Show or change the default Python runtime version.")
+    USAGE_LINE = "default !B![<TAG>]!W!"
+    HELP_TEXT = r"""!G!Default command!W!
+Show or change the default Python version used by the system.
+
+> py default !B![options] [<TAG>]!W!
+
+With no arguments, shows the currently configured default Python version.
+With a !B!<TAG>!W!, sets the default Python version.
+
+!G!Examples:!W!
+> py default
+!W!Shows the current default Python version
+
+> py default 3.13
+!W!Sets Python 3.13 as the default version
+
+> py default 3
+!W!Sets the latest Python 3 as the default version
+"""
+
+    def execute(self):
+        from .default_command import execute
+        execute(self)
+
+
 def load_default_config(root):
     return DefaultConfig(root)
 

src/manage/default_command.py

@@ -0,0 +1,116 @@
+"""Implementation of the 'default' command to manage default Python version."""
+
+import json
+from pathlib import Path as PathlibPath
+
+from .exceptions import ArgumentError, NoInstallsError, NoInstallFoundError
+from .installs import get_installs, get_matching_install_tags
+from .logging import LOGGER
+from .pathutils import Path
+from .tagutils import tag_or_range
+
+
+def _get_default_config_file(install_dir):
+    """Get the path to the default install marker file."""
+    return Path(install_dir) / ".default"
+
+
+def _load_default_install_id(install_dir):
+    """Load the saved default install ID from the marker file."""
+    try:
+        default_file = _get_default_config_file(install_dir)
+        if default_file.exists():
+            return default_file.read_text(encoding="utf-8").strip()
+    except Exception as e:
+        LOGGER.debug("Failed to load default install ID: %s", e)
+    return None
+
+
+def _save_default_install_id(install_dir, install_id):
+    """Save the default install ID to the marker file."""
+    try:
+        default_file = _get_default_config_file(install_dir)
+        default_file.parent.mkdir(parents=True, exist_ok=True)
+        default_file.write_text(install_id, encoding="utf-8")
+        LOGGER.info("Default Python version set to: !G!%s!W!", install_id)
+    except Exception as e:
+        LOGGER.error("Failed to save default install ID: %s", e)
+        raise ArgumentError(f"Could not save default version: {e}") from e
+
+
+def _show_current_default(cmd):
+    """Show the currently configured default Python version."""
+    try:
+        installs = cmd.get_installs(set_default=False)
+    except NoInstallsError:
+        LOGGER.info("No Python installations found.")
+        return
+
+    # Check if there's an explicit default marked
+    default_install = None
+    for install in installs:
+        if install.get("default"):
+            default_install = install
+            break
+
+    if default_install:
+        LOGGER.print("!G!Current default:!W! %s", default_install["display-name"])
+        LOGGER.print("  ID: %s", default_install["id"])
+        LOGGER.print("  Version: %s", default_install.get("sort-version", "unknown"))
+    else:
+        LOGGER.print("!Y!No explicit default set.!W!")
+        LOGGER.print("Using tag-based default: !B!%s!W!", cmd.default_tag)
+
+
+def _set_default_version(cmd, tag):
+    """Set a specific Python version as the default."""
+    try:
+        installs = cmd.get_installs(set_default=False)
+    except NoInstallsError:
+        raise ArgumentError("No Python installations found. Install a version first with 'py install'.") from None
+
+    if not installs:
+        raise ArgumentError("No Python installations found. Install a version first with 'py install'.")
+
+    # Find the install matching the provided tag
+    try:
+        tag_obj = tag_or_range(tag)
+    except Exception as e:
+        raise ArgumentError(f"Invalid tag format: {tag}") from e
+
+    matching = get_matching_install_tags(
+        installs,
+        tag_obj,
+        default_platform=cmd.default_platform,
+        single_tag=False,
+    )
+
+    if not matching:
+        raise NoInstallFoundError(tag=tag)
+
+    selected_install, selected_run_for = matching[0]
+
+    # Save the install ID as the default
+    _save_default_install_id(cmd.install_dir, selected_install["id"])
+
+    LOGGER.info("Default Python version set to: !G!%s!W! (%s)",
+                selected_install["display-name"],
+                selected_install["id"])
+
+
+def execute(cmd):
+    """Execute the default command."""
+    cmd.show_welcome()
+
+    if cmd.show_help:
+        cmd.help()
+        return
+
+    if not cmd.args:
+        # Show current default
+        _show_current_default(cmd)
+    else:
+        # Set new default
+        tag = " ".join(cmd.args[0:1])  # Take the first argument as the tag
+        _set_default_version(cmd, tag)
+

src/manage/installs.py

@@ -117,9 +117,24 @@ def get_installs(
         except LookupError:
             LOGGER.debug("No virtual environment found")
 
+    # Check for a saved default install marker
+    try:
+        default_file = Path(install_dir) / ".default"
+        if default_file.exists():
+            default_id = default_file.read_text(encoding="utf-8").strip()
+            LOGGER.debug("Found saved default install ID: %s", default_id)
+            for install in installs:
+                if install["id"] == default_id:
+                    install["default"] = True
+                    LOGGER.debug("Marked %s as default", default_id)
+                    break
+    except Exception as ex:
+        LOGGER.debug("Could not load default install marker: %s", ex)
+
     return installs
 
 
+
 def _make_alias_key(alias):
     n1, sep, n3 = alias.rpartition(".")
     n2 = ""

tests/test_default_command.py

@@ -0,0 +1,59 @@
+"""Tests for the default command."""
+
+import pytest
+from manage import commands
+from manage.exceptions import ArgumentError, NoInstallsError
+
+
+def test_default_command_help(assert_log):
+    """Test the default command help output."""
+    cmd = commands.DefaultCommand([commands.DefaultCommand.CMD, "--help"], None)
+    cmd.execute()
+    assert_log(
+        assert_log.skip_until(".*Default command.*"),
+    )
+
+
+def test_default_command_no_args_no_installs(assert_log):
+    """Test default command with no arguments and no installations."""
+    cmd = commands.DefaultCommand([commands.DefaultCommand.CMD], None)
+    # This should handle the case gracefully
+    # We expect it to either show a message about no installs or show current default
+    # The actual behavior depends on how get_installs works
+    try:
+        cmd.execute()
+    except NoInstallsError:
+        # This is acceptable - no installs available
+        pass
+
+
+def test_default_command_with_invalid_tag():
+    """Test default command with an invalid tag."""
+    cmd = commands.DefaultCommand([commands.DefaultCommand.CMD, "invalid-tag"], None)
+    try:
+        cmd.execute()
+    except (ArgumentError, NoInstallsError):
+        # Expected - no matching install found or invalid tag
+        pass
+
+
+def test_default_command_args_parsing():
+    """Test that default command properly parses arguments."""
+    cmd = commands.DefaultCommand([commands.DefaultCommand.CMD, "3.13"], None)
+    assert cmd.args == ["3.13"]
+    assert cmd.show_help is False
+
+
+def test_default_command_help_flag():
+    """Test that --help flag is recognized."""
+    cmd = commands.DefaultCommand([commands.DefaultCommand.CMD, "--help"], None)
+    assert cmd.show_help is True
+
+
+def test_default_command_class_attributes():
+    """Test that DefaultCommand has required attributes."""
+    assert commands.DefaultCommand.CMD == "default"
+    assert hasattr(commands.DefaultCommand, "HELP_LINE")
+    assert hasattr(commands.DefaultCommand, "USAGE_LINE")
+    assert hasattr(commands.DefaultCommand, "HELP_TEXT")
+    assert hasattr(commands.DefaultCommand, "execute")