Cheapest Flour |2|
~~~~~~~~~~~~~~~~~~

Your friend Ozan is a great cook and wants to buy some flour in a market
to make some cookies. In this market, all brands of flour is marked with
prices **P** per **W** kilograms instead of 1 kilogram. He does not want
to be overcharged, so you should help him. Can you order all these
brands with their prices per kg in decreasing order?

Write a function named *cheapest_flour* which gets two *string*\ s as
input and output file names. In the input file, each line stands for a
brand and includes two *integers*, **P** and **W** separated by a space
where **P** is the price of the **W** kilograms of this brand. The
function must write the price per kg of each brand in the decreasing
order to the output file.

.. container:: sampleio

   Sample I/O:

.. |2| image:: ../../figures/difficulty_three.png
   :class: difficulty

.. code:: default

   Sample function call:  
       cheapest_flour("input.txt", "output.txt")

   Content of the file "input.txt":  
       12 3
       25 2
       15 6
       23 8
       11 2

   Content of the file "output.txt" after function call:
       12.5
       5.5
       4.0
       2.875
       2.5

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Show the Answer

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In this solution, you will see an example of ``with`` structure in file
handling.

.. code:: python

   with open(...) as f:
     block

is equivalent to

.. code:: python

   f = open(...)
   block
   f.close()

``with`` structure closes the file automatically when the code block in
its scope is terminated for any reason.

.. code:: python

   def cheapest_flour(input_path, output_path):

       prices_per_kg = []

       with open(input_path, 'r') as input_file:     # opening the file in read mode
           for line in input_file.readlines():
               brand = list(map(int,list(line.split())))   # getting integer values in a line.
               price = brand[0]
               weight = brand[1]
               prices_per_kg.append(price/weight)

       prices_per_kg.sort(reverse=True)        # sorting in decreasing order

       with open(output_path, 'w') as output_file:     # opening the file in write mode
           for brand in prices_per_kg:
               output_file.write(str(brand)+"\n") # print values into the file with newlines

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