Grades
======

Consider a list of students where each student is represented by a list with three components:

    - The student's name (:class:`srt`).
    - Whether the student is repeating course or not (:class:`bool`): If the value is ``True`` the student is repeating.
    - A sequence of the student grades (:class:`float` between 0.0 and 10.0). The number of grades is not fixed but it is always greater than 1.

For example:

    .. literalinclude:: grade_classify.test
        :language: python3
        :start-after: --stl-ini
        :end-before: --stl-fi

The **average grade** of a student is defined as the average of all his/her grades but the worst one (ie. the worst grade is discared before computing the average).

You are required to implement the following functions related to a list of students and deliver **all of them** in the same module :mod:`grades` (file :file:`grades.py`).
The weights of these functions are 10%, 40%, 40% and 10% respectively.



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Since the two main functions requested do require the computation of the average as described,
first let's proceed by implementing the following auxiliary fuction:

    .. py:function:: average(st)

such that

    **given** *st* a :class:`list` with the information of a student as described above

    **returns** a :class:`float` with the average value of the student's grade discarding the worst one and rounded to 2 decimals.

For example:

    .. literalinclude:: average.test
        :language: python3
        :start-after: --ini
        :end-before: --fi

Doctests are available in the :download:`average.test` file.

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Now, we first wish to separate the students between those who passed and those who did not.
To that purpose you have to implement the following function:

    .. py:function:: grade_classify(stL)

such that

    **given** *stL* a :class:`list` of lists where each sublist is the information of an student as described above

    **returns** two new :class:`list` s:

        #. the list of the students who passed (the average grade is >= 5.0) in alphabetical order by the student's name.
        #. the list of the students who did not pass also in alphabetical order.

    Both are :class:`list` of :class:`tuple` where each tuple contains the following student's information:

        - a :class:`str` with the student's name
        - a :class:`int` with the student's average grade rounded to 2 decimals.

    The input list should **not be modified**.

For example:

    .. literalinclude:: grade_classify.test
        :language: python3
        :start-after: --ini
        :end-before: --fi

Doctests are available in the :download:`grade_classify.test` file.


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Second, we wish to rank the students from high to low average grade.
To that purpose you have to implement the following function:

    .. py:function:: grade_rank(stL)

such that

    **given** *stL* a :class:`list` of lists where each sublist is the information of an student as described above

    **updates** *stL* by :

        #. Updating every student information by eliminating the information after the student's name and adding a :class:`float` with the student's grades average rounded to 2 decimals **before** the name.
        #. Ordering the students list from high to low average grade.
        #. Adding to every student an :class:`int` at the beginning indicating the grade ranking of the student (starting at 1).

For example:

    .. literalinclude:: grade_rank.test
        :language: python3
        :start-after: --ini
        :end-before: --fi

Doctests are available in the :download:`grade_rank.test` file.

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Third, we wish to select either the students that are repeating or the ones that are new.
To that purpose you have to implement the following function:

    .. py:function:: grade_select(stL, mode)

such that

    **given**

        - *stL* a :class:`list` of lists where each sublist is the information of an student as described above
        - *mode*  a :class:`str`

    **updates** *stL* by leaving only the students that are new if *mode* is ``'new'``, or the ones that are repeating  if *mode* is ``'rep'``. If *mode* is anything else the list *stL* must remain unchanged.

For example:

    .. literalinclude:: grade_select.test
        :language: python3
        :start-after: --ini
        :end-before: --fi

Doctests are available in the :download:`grade_select.test` file.