URL format
==========

Suppose that the format of a web address is:

``scheme://host:port``

as for instance ``http://magraner:1200``, where ``http`` is the scheme, 
always ending with a colon and two slash signs, the host is
``magraner`` and the port is ``1200``.

Write the function :py:func:`check_url` that takes a string with a
web address in url format, and returns another string showing whether
it contains error, following these rules, in the given ordering:

  * If the number of colon sign is not two, the returned string is
    ``'colon error'``

  * If the first character of the scheme is not alphabetical the
    returned string is ``'scheme error'``

  * If any of the characters following the last colon sign is not a
    digit, the returned string is ``'port error'``

In any other case the returned string is ``'correct'``.

Save this function into the file ``url_format.py``. Examples:
   
   .. literalinclude:: test-url_format.txt
      :language: python3
      :lines: 3-
   .. note::

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

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