Number plate
============

We represent a car registration as a string with four digits followed
by a whitespace character and three consonant capital letters.

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

#. Write the function :py:func:`pos_letter` that takes a number
   plate (string) and another string with one character, and returns the
   first position of this character within the three letters group of
   the number plate. If this character is different from all three
   letters then the function will return -1. Examples:
   
   .. literalinclude:: test-numberplate1.txt
      :language: python3
      :lines: 3-

   .. note::
      More tests are provided in the :download:`test-numberplate1.txt<test-numberplate1.txt>` file.
      
          
#. Write the function :py:func:`only_digits` that takes a number
   plate (string), and returns ``True`` if the first four characters of the
   number plate are digits and ``False`` otherwise. Examples:

   .. literalinclude:: test-numberplate2.txt
      :language: python3
      :lines: 3-

   .. note::
      More tests are provided in the :download:`test-numberplate2.txt<test-numberplate2.txt>` file.
      
#. Write function :py:func:`is_upper_consonant`
   that given a string with one character returns ``True`` if this
   character is a uppercase consonant letter and ``False`` otherwise. Examples:

   .. literalinclude:: test-numberplate5.txt
      :language: python3
      :lines: 3-10

   .. note::
      More tests are provided in the :download:`test-numberplate5.txt<test-numberplate5.txt>` file.


#. Write the function :py:func:`only_consonants` that takes a number
   plate (string), and returns ``True`` if the last three characters
   of the number plate are consonant capital letters and ``False``
   otherwise. One way of designing this function is by using function
   :py:func:`is_upper_consonant`. Example:

   .. literalinclude:: test-numberplate3.txt
      :language: python3
      :lines: 3-

   .. note::
      More tests are provided in the :download:`test-numberplate3.txt<test-numberplate3.txt>` file.
      
#. Write the function :py:func:`correct_numberplate` that takes a
   number plate (string), and returns ``True`` if the number plate is
   correct (see definition at the beginning) and ``False`` otherwise.
   **This function must call some of the previous functions**.
   
      See the following examples:

   .. literalinclude:: test-numberplate4.txt
      :language: python3
      :lines: 3-

   .. note::
      More tests are provided in the :download:`test-numberplate4.txt<test-numberplate4.txt>` file.
      
.. rubric:: Solutions

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