Fix errors and issues picked up by type checking

There was a handful of issues where static type
checking either picked up errors or ran into
code that could not verified by the mypy static
type checking. Specifically:

1. in configure.py: Fix a typo in logging (changing
"eror" to "error" that was not covered in our pytest
test cases. This would have resulted in an error
had we hit this condition.

2. in __init__.py: We now always return an integer
from main (so we sys.exit 0 if everything works).
While None being passed into sys.exit isn't an
error in python, it does break static type checking.

3. in __init__.py: We also avoid reusing the variable
name "output" for the subrocess output (bytes) and
the cats output type that goes into the subprocess.
While this isn't an error in python, it does break
static type checking.

cats/__init__.py

@@ -195,7 +195,7 @@ def to_json(self, dateformat: str = "", **kwargs) -> str:
 def schedule_at(output: CATSOutput, args: list[str]) -> None:
     "Schedule job with optimal start time using at(1)"
     proc = subprocess.Popen(args, stdout=subprocess.PIPE)
-    output = subprocess.check_output(
+    proc_output = subprocess.check_output(
         (
             "at",
             "-t",
@@ -205,7 +205,7 @@ def schedule_at(output: CATSOutput, args: list[str]) -> None:
     )
 
 
-def main(arguments=None) -> Optional[int]:
+def main(arguments=None) -> int:
     parser = parse_arguments()
     args = parser.parse_args(arguments)
     if args.command and not args.scheduler:
@@ -263,6 +263,7 @@ def main(arguments=None) -> Optional[int]:
         print(output)
     if args.command and args.scheduler == "at":
         schedule_at(output, args.command.split())
+    return 0
 
 
 if __name__ == "__main__":

cats/configure.py

@@ -47,7 +47,7 @@ def get_runtime_config(args) -> tuple[dict, APIInterface, str, int]:
     try:
         duration = int(args.duration)
     except ValueError:
-        logging.eror(msg)
+        logging.error(msg)
         raise ValueError
     if duration <= 0:
         logging.error(msg)
@@ -91,13 +91,14 @@ def CI_API_from_config_or_args(args, config) -> APIInterface:
         api = "carbonintensity.org.uk"  # default value
         logging.warning(f"Unspecified carbon intensity forecast service, using {api}")
     try:
-        return API_interfaces[api]
+        interface = API_interfaces[api]
     except KeyError:
         logging.error(
             f"Error: {api} is not a valid API choice. It must be one of " "\n".join(
                 API_interfaces.keys()
             )
         )
+    return interface
 
 
 def get_location_from_config_or_args(args, config) -> str: