✨ Add the ability to pass a file on the command line

Closes #1.

Author: davep

src/dhv/__main__.py

@@ -5,6 +5,7 @@
 from argparse import ArgumentParser, BooleanOptionalAction, Namespace
 from inspect import cleandoc
 from operator import attrgetter
+from pathlib import Path
 
 ##############################################################################
 # Local imports.
@@ -66,6 +67,14 @@ def get_args() -> Namespace:
         help="Set the theme for the application (set to ? to list available themes)",
     )
 
+    # An optional file to open.
+    parser.add_argument(
+        "source",
+        nargs="?",
+        type=Path,
+        help="A Python source file to disassemble",
+    )
+
     # The remainder is going to be the initial command.
     parser.add_argument(
         "command",

src/dhv/screens/main.py

@@ -99,10 +99,26 @@ def compose(self) -> ComposeResult:
         yield Disassembly()
         yield Footer()
 
+    def _show_source(self, source: Path) -> None:
+        """Load up the content of a Python source file.
+
+        Args:
+            source: The path to the source file to load.
+        """
+        try:
+            self.query_one(Source).load_text(source.read_text())
+        except IOError as error:
+            self.notify(str(error), title=f"Unable to load {source}", severity="error")
+            return
+        with update_configuration() as config:
+            config.last_load_location = str(source.absolute().parent)
+
     def on_mount(self) -> None:
         """Configure the display once the DOM is mounted."""
         self.query_one(Disassembly).show_offset = load_configuration().show_offsets
         self.query_one(Disassembly).show_opcodes = load_configuration().show_opcodes
+        if isinstance(to_open := self._arguments.source, Path):
+            self._show_source(to_open)
 
     def _watch_horizontal_layout(self) -> None:
         """React to the horizontal layout setting being changed."""
@@ -133,7 +149,7 @@ def action_new_code_command(self) -> None:
 
     @work
     async def action_load_file_command(self) -> None:
-        """Load the content of a file."""
+        """Browse for and open a Python source file."""
         if not (
             start_location := Path(load_configuration().last_load_location or ".")
         ).is_dir():
@@ -153,13 +169,7 @@ async def action_load_file_command(self) -> None:
                 ),
             )
         ):
-            try:
-                self.query_one(Source).load_text(python_file.read_text())
-            except IOError as error:
-                self.notify(str(error), title="Unable to load that file")
-                return
-            with update_configuration() as config:
-                config.last_load_location = str(python_file.absolute().parent)
+            self._show_source(python_file)
 
     def action_switch_layout_command(self) -> None:
         """Switch the layout of the window."""