Enhance can.logger to consider the append option

can/logger.py

@@ -31,9 +31,10 @@ def _create_base_argument_parser(parser: argparse.ArgumentParser) -> None:
     parser.add_argument(
         "-c",
         "--channel",
-        help='''Most backend interfaces require some sort of channel.
-    For example with the serial interface the channel might be a rfcomm device: "/dev/rfcomm0"
-    With the socketcan interfaces valid channel examples include: "can0", "vcan0"''',
+        help=r"Most backend interfaces require some sort of channel. For "
+        r"example with the serial interface the channel might be a rfcomm"
+        r' device: "/dev/rfcomm0". With the socketcan interface valid '
+        r'channel examples include: "can0", "vcan0".',
     )
 
     parser.add_argument(
@@ -60,11 +61,10 @@ def _create_base_argument_parser(parser: argparse.ArgumentParser) -> None:
     parser.add_argument(
         "extra_args",
         nargs=argparse.REMAINDER,
-        help="""\
-        The remaining arguments will be used for the interface initialisation.
-        For example, `-i vector -c 1 --app-name=MyCanApp` is the equivalent to 
-        opening the bus with `Bus('vector', channel=1, app_name='MyCanApp')`
-        """,
+        help=r"The remaining arguments will be used for the interface "
+        r"initialisation. For example, `-i vector -c 1 --app-name="
+        r"MyCanApp` is the equivalent to opening the bus with `Bus("
+        r"'vector', channel=1, app_name='MyCanApp')",
     )
 
 
@@ -82,8 +82,10 @@ def _append_filter_argument(
         *args,
         "--filter",
         help="R|Space separated CAN filters for the given CAN interface:"
-        "\n      <can_id>:<can_mask> (matches when <received_can_id> & mask == can_id & mask)"
-        "\n      <can_id>~<can_mask> (matches when <received_can_id> & mask != can_id & mask)"
+        "\n      <can_id>:<can_mask> (matches when <received_can_id> & mask =="
+        " can_id & mask)"
+        "\n      <can_id>~<can_mask> (matches when <received_can_id> & mask !="
+        " can_id & mask)"
         "\nFx to show only frames with ID 0x100 to 0x103 and 0x200 to 0x20F:"
         "\n      python -m can.viewer -f 100:7FC 200:7F0"
         "\nNote that the ID and mask are always interpreted as hex values",
@@ -141,7 +143,8 @@ def _parse_additonal_config(unknown_args):
 
 def main() -> None:
     parser = argparse.ArgumentParser(
-        description="Log CAN traffic, printing messages to stdout or to a given file.",
+        description="Log CAN traffic, printing messages to stdout or to a "
+        "given file.",
     )
 
     _create_base_argument_parser(parser)
@@ -159,10 +162,25 @@ def main() -> None:
         "--file_size",
         dest="file_size",
         type=int,
-        help="Maximum file size in bytes. Rotate log file when size threshold is reached.",
+        help="Maximum file size in bytes. Rotate log file when size threshold "
+        "is reached.",
         default=None,
     )
 
+    parser.add_argument(
+        "-a",
+        "--append",
+        # "action"=argparse.BooleanOptionalAction,  # Use when Python>=3.9
+        dest="append_mode",
+        type=bool,
+        help="A boolean option for whether to overwrite or append to an "
+        "existing log file if it exists. To append to an existing log "
+        "file, pass `True` or `1`. To overwrite an existing log file, "
+        "pass `False`, `0`, or do not add the -a argument. E.g. -a True "
+        "or -a False.",
+        default=False,
+    )
+
     parser.add_argument(
         "-v",
         action="count",
@@ -201,12 +219,42 @@ def main() -> None:
     print(f"Connected to {bus.__class__.__name__}: {bus.channel_info}")
     print(f"Can Logger (Started on {datetime.now()})")
 
+    # argparser.py in Python 3.7.11 does not properly consider boolean
+    # arguments passed in from the command line. If a boolean is passed in,
+    # the variable must be converted to an integer 0 (False) or 1 (True).
+    # Once the project goes to a minimum of Python 3.9, the
+    # `BooleanOptionalAction` can be used and the following code block will no
+    # longer be required (Please do not use this as a reason to advocate a
+    # minimum Python version of 3.9).
+    boolean_args = ["-a", "--append"]
+    args = sys.argv[1:]
+    for _, bool_arg in enumerate(boolean_args):
+        for j, arg in enumerate(args):
+            if bool_arg == arg:
+                # Make sure the length of args is long enough to check the
+                # toggle, e.g. stop an index error from occurring.
+                # argparse.py should have already caught this, but this is a
+                # double check.
+                if len(args) - 1 >= j + 1:
+                    toggle = args[j + 1]
+                else:
+                    break
+                # Consider the action, and update the results to accurately
+                # embody request.
+                if toggle in ("0", "False"):
+                    results.append_mode = False
+                elif toggle in ("1", "True"):
+                    results.append_mode = True
+                else:
+                    pass
+
+    options = {"append": results.append_mode}
     if results.file_size:
         logger = SizedRotatingLogger(
-            base_filename=results.log_file, max_bytes=results.file_size
+            base_filename=results.log_file, max_bytes=results.file_size, **options
         )
     else:
-        logger = Logger(filename=results.log_file)  # type: ignore
+        logger = Logger(filename=results.log_file, **options)  # type: ignore
 
     try:
         while True: