.. py:module::pH_measure 

pH Measure
==========

A corporation uses files to store several measurements of the pH of
its products. In these files, each line records the data of one
product and contains the name of the product and a varying number of
pH measurements for that product, all separated by commas. As an
example, you can download file
:download:`ph_data.txt<examples/ph_data.txt>` which has the following
content:

.. literalinclude:: examples/ph_data.txt
   :language: text

Write function :py:func:`ph_average` that takes the name of a file as
that described above and a tolerance ``epsilon``, and returns a list
with the names of the products that have an average of measurements
that indicate a neutral pH, that is, a pH of 7. To check the
equality between two values you have to do the comparison with the
given tolerance ``epsilon``, i. e., check if the absolute
value of the difference of the values is lower than ``epsilon``. The
list must be sorted lexicographically.

Save this function in file ``ph_measure.py``. Examples:

   .. literalinclude:: test-ph_average.txt
      :language: python3
      :lines: 17-20


.. rubric:: Solution

A solution is provided in file :download:`ph_measure.py<solution/ph_measure.py>`.