Loop to Efficiently Populate Class Attributes

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February 12th, 2013, 03:11 PM

JohnPetrucci00

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Loop to Efficiently Populate Class Attributes

Hello,

I am starting to get into classes in Python and have the following case:

I am reading a CSV file with 61 columns (each column with a unique header label). I created a class with 61 attributes (I apologize if I'm using the terms incorrectly). A portion of the class is below:

Code:

class partProperties:
    def setPartID(self, number):
        self.partID = number
    def setPartName(self, text):
        self.partName = text

Only 2 of the 61 functions are shown. I would like to read each row of the CSV and 'automatically' set the attributes for a new instance of this class (each row will be an instance). The list of attributes in the class is in the same order as the columns in the CSV.

My question: is there a way to set all of the attributes without typing each unique call (i.e. 'setPartID')? Ideally I would like to index each attribute so I can loop through all of them as I read each row of the CSV. Is this possible? How would an experienced programmer approach this?

Thanks.

-John

February 12th, 2013, 07:08 PM

b49P23TIvg

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This answer is ridiculous.

The attributes of the class are data driven. Why are the generic objects better than dictionaries? I can't think of a reason. One could insert a price method that depends on item featues, and that would be a good reason to use a custom class instead of a dictionary. The class is restrictive, the keys need to be valid python identifiers.

Code:

import io
import sys
import csv
import pprint

class generic(dict):
    pass

def generic_factory(file_object):
    reader = iter(csv.reader(file_object))
    attributes = next(reader)
    result = []
    try:
        while True:
            row = next(reader)
            kwargs = dict(zip(attributes,row))
            result.append(generic(**kwargs))
    except StopIteration:
        pass
    return result

DATA = '"partID","partName"\n35553,"snare"\n28709,"rim"\n85332,"skin"'

if sys.version[0] == '2':
    DATA = DATA.decode('utf8')

FAKEFILE = io.StringIO(DATA)

FAKEFILE.seek(0)

OBJECTS = generic_factory(FAKEFILE)

FAKEFILE.close()

pprint.pprint([str(O) for O in OBJECTS])

It occurs to me this is easier:

Code:

import io
import sys
import csv
import pprint

DATA = '"partID","partName"\n35553,"snare"\n28709,"rim"\n85332,"skin"'

if sys.version[0] == '2':
    DATA = DATA.decode('utf8')

with io.StringIO(DATA) as FAKEFILE:
    FAKEFILE.seek(0)
    OBJECTS = [O for O in csv.DictReader(FAKEFILE)]

pprint.pprint([str(O) for O in OBJECTS])

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Last edited by b49P23TIvg : February 12th, 2013 at 07:10 PM.

February 13th, 2013, 09:42 AM

JohnPetrucci00

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Thank you very much for the response. I am impressed how concise the code is to read the CSV into a dictionary. I need to spend some time studying your code to understand it.

The challenge I'm facing is that each CSV file that is read may contain only a subset of the 61 columns in the 'master' header.

If I decide to go the class route, is there a way of defining new instances on the fly from a dynamic variable name?

For example, as each row is read, the instances are created and named:

'part-1'
'part-2'
'part-3'

From what I've seen, it appears I may need to use eval for this?

-John

February 13th, 2013, 10:30 AM

JohnPetrucci00

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Join Date: Dec 2012

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After experimenting, it seems that the following code accomplishes instantiation from dynamic variable names:

Code:

partObjectNames.insert(i, 'line-' + str(i) + '-part')	# Create the name of the object to hold the extracted inputs
partObjectNames[i] = partProperties(extractedInputs)	# Instantiate the object

Loop to Efficiently Populate Class Attributes

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