Add the main flow that prints the results of the lectures

Task: MIL-004#3

src/weather/__main__.py

@@ -0,0 +1,108 @@
+## @file __main__.py
+#  @brief Command line of the weather data project: `python -m weather`.
+#
+#  Prints the results of both lectures in the order of the lectures. The csv
+#  part needs no third-party package; the pandas part needs the `pandas` extra.
+#  A file is written only when `--export PATH` is given.
+
+"""Prints the results of the weather lectures; run with `python -m weather`."""
+
+import argparse
+import sys
+from collections.abc import Sequence
+from pathlib import Path
+
+from weather.constants import MONDAY, PANDAS_MISSING_MESSAGE
+from weather.csv_reader import read_rows, read_temperatures
+
+## @brief Value that `main` returns when the run succeeded.
+EXIT_OK = 0
+
+## @brief Value that `main` returns when the optional pandas extra is missing.
+EXIT_PANDAS_MISSING = 1
+
+
+def _build_parser() -> argparse.ArgumentParser:
+    """! @brief Build the command line parser with its one optional flag.
+
+    @return The parser of `python -m weather`.
+    """
+    parser = argparse.ArgumentParser(
+        prog="weather",
+        description="Print the results of the weather data lectures.",
+    )
+    parser.add_argument(
+        "--export",
+        metavar="PATH",
+        type=Path,
+        default=None,
+        help="also write the scores table to this CSV file",
+    )
+    return parser
+
+
+def _print_csv_part() -> None:
+    """! @brief Print the rows and temperatures read with the csv library."""
+    print("Rows (csv library):")
+    for row in read_rows():
+        print(row)
+    print(f"Temperatures (csv library): {read_temperatures()}")
+
+
+def _print_pandas_part(export_path: Path | None) -> None:
+    """! @brief Print the pandas results and export the scores when asked.
+
+    @param export_path File to write the scores table to; `None` writes nothing.
+    @throws ImportError When `pandas` is not installed.
+    """
+    # Imported here so that the csv part runs without the optional extra.
+    from weather.analysis import (
+        average_temp,
+        average_temp_mean,
+        day_in_fahrenheit,
+        hottest_row,
+        max_temp,
+        read_data,
+        row_for_day,
+        to_data_dict,
+        to_temp_list,
+    )
+    from weather.export import create_scores_frame, export_frame
+
+    data = read_data()
+    print(f"Data frame (pandas):\n{data}")
+    print(f"Data dict: {to_data_dict(data)}")
+    print(f"Temp list: {to_temp_list(data)}")
+    print(f"Average temperature (sum / len): {average_temp(data)}")
+    print(f"Average temperature (mean): {average_temp_mean(data)}")
+    print(f"Maximum temperature: {max_temp(data)}")
+    print(f"Row of {MONDAY}:\n{row_for_day(data, MONDAY)}")
+    print(f"Hottest row:\n{hottest_row(data)}")
+    print(f"{MONDAY} in Fahrenheit: {day_in_fahrenheit(data, MONDAY)}")
+    scores = create_scores_frame()
+    print(f"Scores frame (from a dictionary):\n{scores}")
+    if export_path is not None:
+        export_frame(scores, export_path)
+        print(f"Scores frame exported to: {export_path}")
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    """! @brief Print the results of the lectures and optionally export a table.
+
+    @param argv The command line arguments; `sys.argv[1:]` when `None`.
+    @return `0` on success, `1` when the pandas extra is not installed.
+    """
+    args = _build_parser().parse_args(argv)
+    _print_csv_part()
+    try:
+        _print_pandas_part(args.export)
+    except ImportError as error:
+        if error.name != "pandas":
+            raise
+        print(PANDAS_MISSING_MESSAGE, file=sys.stderr)
+        return EXIT_PANDAS_MISSING
+    return EXIT_OK
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())