Question

I am trying to read in a CSV file that looks like this:

ruby,2,100
diamond,1,400
emerald,3,250
amethyst,2,50
opal,1,300
sapphire,2,500
malachite,1,60

Here is some code I have been experimenting with.

class jewel:
    def __init__(gem, name, carat, value):
            gem.name = name
            gem.carot = carat
            gem.value = value
    def __repr__(gem):
            return repr((gem.name, gem.carat, gem.value))

jewel_objects = [jewel('diamond', '1', 400),
                 jewel('ruby', '2', 200),
                 jewel('opal', '1', 600),
                ]

aList = [sorted(jewel_objects, key=lambda jewel: (jewel.value))]
print aList

I would like to read in the values and assign them to name, carat, and value but I’m not sure how to do so. Then once I get them read in I would like to sort them by value per carat so value/carat. I have done quite a bit of searching and have came up blank. Thank you very much for your help in advance.

Answer 1

You need to do two things here, the first is actually loading the data into the objects. I recommend you look at the ‘csv’ module in the standard python library for this. It’s very complete and will read each row and make it easily accessable

CSV docs: http://docs.python.org/library/csv.html

I would create a list of the objects, and then implement either an cmp function in your object, or (if you’re using an older version of python) you can pass a function to sorted() that would define it. You can get more info about sorting in the python wiki

Wiki docs: http://wiki.python.org/moin/HowTo/Sorting

You would implement the cmp function like this in your class (this can be made a bit more efficent, but I’m being descriptive here)

def __cmp__(gem, other):
    if (gem.value / gem.carot) < (other.value / other.carot):
        return -1
    elif (gem.value / gem.carot) > (other.value / other.carot): 
        return 1
    else:
        return 0