Python: implement --tzname for CLI

src/python/scripts/lon_tz.py

@@ -125,7 +125,7 @@ def _do_tzfile() -> None:
 
 
 def _do_lon_tz(args: dict) -> ErrStr | None:
-    """call timezone_solar to generate time zone from parmeters on command line"""
+    """call TimeZoneSolar to generate time zone from parmeters on command line"""
     err = None
 
     # collect parameters
@@ -142,7 +142,7 @@ def _do_lon_tz(args: dict) -> ErrStr | None:
             case "longitude":
                 tzs_params["use_lon_tz"] = True
 
-    # instantiate timezone_solar object and print requested field
+    # instantiate TimeZoneSolar object and print requested field(s)
     tzs = TimeZoneSolar(**tzs_params)
     try:
         get_keys = (','.join(args["get"])).split(sep=',')
@@ -157,6 +157,27 @@ def _do_lon_tz(args: dict) -> ErrStr | None:
 
     return err
 
+
+def _do_named_tz(args: dict) -> ErrStr | None:
+    """call TimeZoneSolar to generate date for a named time zone"""
+    err = None
+
+    # instantiate TimeZoneSolar object and print requested field(s)
+    tzname = args["tzname"]
+    tzs = TimeZoneSolar(tzname=tzname)
+    try:
+        get_keys = (','.join(args["get"])).split(sep=',')
+        for get_key in get_keys:
+            value = tzs.get(get_key)
+            if value is None:
+                print("")
+            else:
+                print(value)
+    except ValueError as tz_exc:
+        err = str(tz_exc)
+
+    return err
+
 #
 # command-line parsing functions
 #
@@ -184,7 +205,7 @@ def _gen_arg_parser() -> argparse.ArgumentParser:
         help="turn on debugging mode",
     )
 
-    # mutually-exclusive arguments: --tzfile and --longitude
+    # mutually-exclusive arguments: --tzfile, --tzname and --longitude
     excl_group = top_parser.add_mutually_exclusive_group(required=True)
 
     # --tzfile/tzdata flag triggers output of tzdata file and ends program
@@ -195,14 +216,21 @@ def _gen_arg_parser() -> argparse.ArgumentParser:
         help="generate solar time zones tzdata text",
     )
 
+    # --tzname sets a name for a specified time zone, no other parameters allowed when this is used
+    excl_group.add_argument(
+        "--tzname",
+        type=str,
+        help="name of a specific solar time zone (mutually exclusive with --tzfile & --longitude)",
+    )
+
     # --longitude sets degrees of longitude for a specified time zone
     excl_group.add_argument(
         "--longitude",
         type=float,
-        help="longitude for solar time zone (required when not using --tzfile)",
+        help="longitude for solar time zone (mutually exclusive with --tzfile & --tzname)",
     )
 
-    # parameters for timezone_solar
+    # parameters for TimeZoneSolar
     top_parser.add_argument(
         "--latitude",
         type=float,
@@ -218,7 +246,7 @@ def _gen_arg_parser() -> argparse.ArgumentParser:
     top_parser.add_argument(
         "--get",
         action='append',
-        help="specify solar time zone field to output",
+        help="specify solar time zone field(s) for output",
     )
 
     return top_parser
@@ -249,6 +277,8 @@ def main():
         # call function named in argument parser settings with a dictionary of the CLI arguments
         if "tzfile" in args and args["tzfile"] is True:
             _do_tzfile()
+        elif "tzname" in args and args["tzname"] is not None:
+            err = _do_named_tz(args)
         else:
             err = _do_lon_tz(args)
     except Exception as exc:

src/python/timezone_solar/timezone_solar.py

@@ -111,13 +111,43 @@ def _tz_params_latitude(cls, tz_params):
         # no effects on results from latitude between 80° north & south
         return None
 
+    # generate time zone parameters from given time zone name
+    @classmethod
+    def _tz_name2params(cls, tzname: str) -> dict:
+        match = re.fullmatch(r"^Lon(\d{3})([EW])$", tzname, flags=re.IGNORECASE)
+        if match:
+            is_west = match.group(2) == "W"
+            longitude = int(match.group(1)) * (-1 if is_west else 1)
+            if abs(int(longitude)) > 180:
+                raise ValueError(f"longitude {longitude} is out of bounds ±180")
+            use_lon_tz = True
+            return {"longitude": longitude, "use_lon_tz": use_lon_tz}
+        match = re.fullmatch(r"^(East|West)(\d{2})$", tzname, flags=re.IGNORECASE)
+        if match:
+            is_west = match.group(1) == "West"
+            hour_num = int(match.group(2))
+            if hour_num > 12:
+                raise ValueError(f"time zone hour {hour_num} is out of bounds ±12")
+            longitude = hour_num * 15 * (-1 if is_west else 1)
+            if abs(int(longitude)) > 180:
+                raise ValueError(f"longitude {longitude} is out of bounds ±180")
+            use_lon_tz = False
+            return {"longitude": longitude, "use_lon_tz": use_lon_tz}
+        raise ValueError(f"{tzname}  is not a valid solar/natural time zone name")
+
     # get timezone parameters (name and minutes offset) - called by __new__()
     @classmethod
-    def _tz_params(cls, tz_params) -> dict:
+    def _tz_params(cls, tz_params: dict) -> dict:
+
+        # rewrite parameters based on time zone if a tzname was provided
+        if "tzname" in tz_params and tz_params["tzname"] is not None:
+            tz_params = cls._tz_name2params(tz_params["tzname"])
+
+        # longitude is required
         if "longitude" not in tz_params:
             raise ValueError("_tz_params: longitude parameter missing")
 
-        # set time zone from longitude and latitude
+        # set time zone from longitude and latitude, if latitude was provided
         if "latitude" in tz_params and tz_params["latitude"] is not None:
             lat_params = cls._tz_params_latitude(tz_params)
             if lat_params is not None: