Import Data Into Namedtuple in Python

Question

I am trying to import data into namedtuple. The data is very large and I need to import it efficiently. I am trying

myData = namedtuple('myData', 'div, name, val')

csv.register_dialect('mycsv', delimiter='\t', quoting=csv.QUOTE_NONE)

with open('demand.txt', 'rb') as f:
     reader = csv.reader(f,'mycsv')

after this point:

• What should I do to import the whole table in demand.txt into a namedtuple in bulk? I see some solutions with for loop but I guess that is inefficient.

• I want to be able to obtain the all values under a field, like when I type data.div? Should the correct format be tuples of namedtuples?

Answer 1

To get a list of myData tuples, do:

data = map(myData._make, reader) # or [myData._make(r) for r in reader]

To get all the values of a particular field:

from operator import attrgetter
data_divs = map(attrgetter('div'), data) # or [r.div for r in data]

However, if you're concerned about efficiency, you should be aware that using attribute access with namedtuples is several times slower than indexed access. This will be faster:

from operator import itemgetter
div_idx = myData._fields.index('div')
data_divs = map(itemgetter(div_idx), data) # or [r[div_idx] for r in data]

Both produce the same list of values.

Answer 2

Please see my sample code snippet below using namedtuple.

from csv import reader
from collections import namedtuple

saleRecord = namedtuple('saleRecord','shopId saleDate totalSales totalCustomers')
fileHandle = open("salesRecord.csv","r")
csvFieldsList=csv.reader(fileHandle)
for fieldsList in csvFieldsList:
    shopRec = saleRecord._make(fieldsList)
    overAllSales += shopRec.totalSales;

print("Total Sales of The Retail Chain =",overAllSales)

Please refer my article on Python collections in my blog at: https://techietweak.wordpress.com/2015/11/11/python-collections/

Hope this helps.