src/weather/constants.py

@@ -3,8 +3,9 @@
 #
 #  Every value that the day-25 lectures fix lives here, so that no other module
 #  contains a magic string or number: the name of the data file, the names of
-#  its columns, the factors of the Fahrenheit conversion and the name of the
-#  exported file.
+#  its columns, the factors of the Fahrenheit conversion, the name of the
+#  exported file, the table that is created from a dictionary and the message
+#  for a missing optional dependency.
 
 """Constants of the weather data project, as fixed by the day-25 lectures."""
 
@@ -46,3 +47,24 @@ FAHRENHEIT_DENOMINATOR: Final[int] = 5
 
 ## @brief Offset of the Celsius to Fahrenheit conversion: `temp * 9 / 5 + 32`.
 FAHRENHEIT_OFFSET: Final[int] = 32
+
+## @brief Name of the column that holds the student names of the lecture's table.
+COLUMN_STUDENTS: Final[str] = "students"
+
+## @brief Name of the column that holds the scores of the lecture's table.
+COLUMN_SCORES: Final[str] = "scores"
+
+## @brief Student names of the table that the lecture creates from a dictionary.
+STUDENTS: Final[tuple[str, ...]] = ("Amy", "James", "Angela")
+
+## @brief Scores of the students, in the order of `STUDENTS`.
+SCORES: Final[tuple[int, ...]] = (76, 56, 65)
+
+## @brief Name of the day that the main flow selects and converts.
+MONDAY: Final[str] = "Monday"
+
+## @brief Message printed when `pandas`, an optional extra, is not installed.
+PANDAS_MISSING_MESSAGE: Final[str] = (
+    "pandas is not installed; the pandas part needs the extra: "
+    'pip install "weather[pandas]"'
+)

src/weather/export.py

@@ -0,0 +1,39 @@
+## @file export.py
+#  @brief Creates a `DataFrame` from a dictionary and exports it to a CSV file.
+#
+#  This is the end of the second lecture: the table of students and scores is
+#  built from a dictionary and written with `DataFrame.to_csv`. Nothing is
+#  written unless `export_frame` is called with a path or its default name.
+
+"""Creates a DataFrame from a dictionary and exports it to a CSV file."""
+
+from pathlib import Path
+
+import pandas
+
+from weather.constants import (
+    COLUMN_SCORES,
+    COLUMN_STUDENTS,
+    EXPORT_FILE_NAME,
+    SCORES,
+    STUDENTS,
+)
+
+
+def create_scores_frame() -> pandas.DataFrame:
+    """! @brief Create the table of students and scores from a dictionary.
+
+    @return A table with the columns `students` and `scores`, one row per student.
+    """
+    data_dict = {COLUMN_STUDENTS: list(STUDENTS), COLUMN_SCORES: list(SCORES)}
+    return pandas.DataFrame(data_dict)
+
+
+def export_frame(frame: pandas.DataFrame, path: Path | str = EXPORT_FILE_NAME) -> None:
+    """! @brief Write a table to a CSV file, the row index included.
+
+    @param frame The table to write.
+    @param path Path of the file to write; `new_data.csv` in the working folder
+           by default.
+    """
+    frame.to_csv(path)

tests/test_constants.py

@@ -34,3 +34,18 @@ def test_fahrenheit_factors_give_the_lecture_formula() -> None:
 
 def test_exported_file_has_the_name_of_the_lecture() -> None:
     assert constants.EXPORT_FILE_NAME == "new_data.csv"
+
+
+def test_scores_table_has_the_columns_and_values_of_the_lecture() -> None:
+    assert constants.COLUMN_STUDENTS == "students"
+    assert constants.COLUMN_SCORES == "scores"
+    assert constants.STUDENTS == ("Amy", "James", "Angela")
+    assert constants.SCORES == (76, 56, 65)
+
+
+def test_main_flow_uses_monday() -> None:
+    assert constants.MONDAY == "Monday"
+
+
+def test_missing_pandas_message_names_the_extra() -> None:
+    assert 'pip install "weather[pandas]"' in constants.PANDAS_MISSING_MESSAGE