Students
========

Save all functions into the same file named ``students.py``.

To manage the class lists of a school year we use a dictionary
:class:`dict` where the key is a 3-tuple with the name and the two
surnames of the student (:class:`str`), and the associated value is
the :class:`list` of subjects in which they are enrolled. For example,
the following dictionary:

.. code:: python

   dic = {('Joan', 'Rubio', 'Boix'): ['Programming', 'Physics', 'Calculus'],
          ('Anna', 'Pons', 'Adell'): ['Calculus', 'Programming']}

contains the student ``Joan Rubio Boix`` enrolled in ``Programming``,
``Physics`` and ``Calculus`` and the student ``Anna Pons Adell``
enrolled in ``Programming`` and ``Calculus``.

#. Write the **modifier** function :py:func:`add_student` that given a
   dictionary as that described, the name and two surnames of a new
   student (:class:`str`), and a :class:`list` with the subjects in
   which they are enrolled, **modifies** the dictionary by adding this new
   student. Examples:
                 
   .. literalinclude:: test-students1.txt
       :language: python
       :lines: 3-
   
   .. Note::

      More tests are provided in :download:`test-students1.txt`.

              
#. Write the function :py:func:`subject_student` that given a
   dictionary as that described, and the name and two surnames of a
   new student (:class:`str`), returns the :class:`list` of subjects
   in which that student is enrolled. If the student isn't in the
   dictionary it returns an empty list. Examples:
                 
   .. literalinclude:: test-students2.txt
       :language: python
       :lines: 3-
   
   .. Note::

      More tests are provided in :download:`test-students2.txt`.
   

#. Write the function :py:func:`listed` that given a dictionary as
   that described and a subject (:class:`str`), returns the
   :class:`list` of all the students enrolled in this subject. In this
   list, a student must be represented with a string following this
   pattern: the first surname, a space, the second surname, a comma
   and a space, and the name. The list has to be sorted by the first
   surname. If no student is enrolled in the given subject, the
   function will return an empty list. Examples:
 
   .. literalinclude:: test-students3.txt
       :language: python
       :lines: 3-
   
   .. Note::

      More tests are provided in :download:`test-students3.txt`.
              
#. Write the function :py:func:`students_per_subject` that given a
   dictionary as that described, returns another dictionary where the
   key is the name of a subject, and its associate value is the number
   of students enrolled in this subject. Examples:
                 
   .. literalinclude:: test-students4.txt
       :language: python
       :lines: 3-
   
   .. Note::

      More tests are provided in :download:`test-students4.txt`.
   
.. rubric:: Solution
      
A solution is provided in the :download:`students.py<solutions/students.py>`