Screw
=====

We represent the code of a screw thread as a string that begins with
the character ``'M'``, then follows its diameter (``int``), a hyphen,
the thread pitch (``float``), the character 'x' and the screw length
(``int``). All measures are in mm. For example, the thread code
``'M3-0.50x10'`` stands for a thread with a 3mm diameter, a pitch of
0.5mm, and a length of 10 mm. A code is incorrect if it does not begin
with the character ``'M'`` or if it does not contain the characters
``'-'`` or ``'x'`` or they are not in the correct order (``'-'``
before ``'x'``).

Write a function :py:func:`screw` that takes a string with a thread
code, and returns its measures (diameter, pitch and length). If the
code is not correct, then the function must return the string ``'code
error'``.

Save this function into the file named ``screw.py``. Examples:

   .. literalinclude:: test-screw.txt
      :language: python3
      :lines: 3-
             
   .. note::

       More tests are provided in the :download:`test-screw.txt<test-screw.txt>` file.

.. rubric:: Solution
      
A solution of these functions is provided in the
:download:`screw.py<solutions/screw.py>` file.